Antitheft system for vehicle

ABSTRACT

It is possible to start engine economically and easily without deteriorating the theft prevention function even when an engine start key is lost. A vehicle theft prevention system includes permission tools ( 5 C,  5 D) for permitting rewrite or write-in of an ID code. The system has a start key registration function for corresponding the ID code of an engine key ( 5 ) to the ID code of an immobilizer control section ( 17 ), so that the engine key ( 5 ) functions as an engine start key ( 5 A,  5 B) when the ID code of the permission tools ( 5 C,  5 D) is correlated with the ID code recorded in the immobilizer control section ( 17 ) and matching is established. Accordingly, when the engine start key is lost or the like, a new engine start key is created for starting the engine economically and easily without requiring replacement of the entire theft prevention device.

TECHNICAL FIELD

The present invention relates to an antitheft system for a work machinesuch as a backhoe or other vehicles.

BACKGROUND ART

A conventional antitheft system for a vehicle employs a technique todisable an engine from being started by an invalid engine start key, inwhich only when an ID code recorded in an engine start key coincideswith an ID code recorded on a vehicle side (immobilizer control unit),the starting of the engine is allowed (see, for example,JP-A-2001-146148, JP-A-10-82223, JP-A-10-129421, JP-A-2000-335370). Inthis system, even if a duplicate key is formed, since the ID codes donot coincide with each other, it becomes impossible to start the engineof the vehicle.

Incidentally, some work machines (vehicles) such as backhoes exemplifiedas rotary work machines are provided with engines as power sources tocause the work machines run. Also in this type of work machine, it isconceivable that an antitheft device similar to the case of anautomobile is incorporated, and also in this case, when the engine isstarted by a valid engine start key, the starting of the engine isallowed, and when the engine is started by an invalid start key, thestarting of the engine can be prevented. Further, different from theautomobile, in the case of the work machine such as the backhoe, acommon engine key is generally used as an engine key to start engines ofplural work machines, so that one engine key can start the engines ofplural work machines. Accordingly, it is important to protect the workmachines from theft by ID codes.

However, in the conventional system, in the case where an engine startkey registered in an immobilizer control unit is lost, since it isimpossible to newly form an engine start key for enabling the startingof the engine of the vehicle with using a commercially available enginekey, the whole antitheft device must be replaced, and this is noteconomical and inconvenient. On the other hand, if an engine start keyfor enabling the starting of the engine of the vehicle can be newlyeasily formed with using a commercially available engine key, therearises a problem that the antitheft function is impaired.

In view of the above problems, the present invention has an object toprovide an antitheft system for a vehicle in which even in the casewhere an engine start key is lost, the engine can be startedeconomically and conveniently without ruining the antitheft function.

DISCLOSURE OF THE INVENTION

According to technical means of the invention to solve the abovetechnical problem, in an antitheft system for a vehicle configured tocollaet an ID code of an engine start key with an ID code recorded in animmobilizer control unit, and to allow starting of an engine by theengine start key when the result of the collation is affirmative,

an allowance tool for allowing rewriting or writing of an ID code isprovided separately from the engine start key, and

a start key registration function is provided for collating an ID codeof the allowance tool with the ID code recorded in the immobilizercontrol unit, and rendering an ID code of an engine key corresponding tothe ID code of the immobilizer control unit when the result of thecollation is affirmative, so that the engine key serves as the enginestart key.

According to another technical means of the invention, in an antitheftsystem for a vehicle configured to collate an ID code of an engine startkey with an ID code recorded in an immobilizer control unit, and toallow starting of an engine by the engine start key when the result ofthe collation is affirmative, or to prevent starting of the engine bythe engine start key when the result of the collatin is negative,

an allowance key for allowing rewriting or writing of an ID code isprovided separately from the engine start key, and

a start key registration function is provided for collating an ID codeof the allowance key with the ID code recorded in the immobilizercontrol unit, and rendering an ID code of an engine key corresponding tothe ID code of the immobilizer control unit when the result of collationis affirmative, so that the engine key serves as the engine start key.

According to yet another technical means of the invention, in anantitheft system for a vehicle configured to collate an ID code of anengine start key with an ID code recorded in an immobilizer controlunit, and to allow starting of an engine by the engine start key whenthe result of the collation is affirmative, or to prevent starting ofthe engine by the engine start key when the result of the collation isnegative,

an allowance key for allowing rewriting or writing of an ID code isprovided, a start key registration function is provided for collating anID code of the allowance key with the ID code recorded in theimmobilizer control unit, and rendering an ID code of an engine keycorresponding to the ID code of the immobilizer control unit when theresult of the collation is affirmative, so that the engine key serevesas the engine start key, and

a cryptographic code for specifying the engine key and an discriminationcode for distinguishing the kind of the engine key are recorded as IDcodes in the engine key and the immobilizer control unit, and thediscrimination code enables the system to distinguish the engine startkey for starting the engine and the allowance key for allowing therewriting or writing of the ID codes.

Further, according to another technical means of the invention, in thestart key registration function, after the allowance key is insertedinto a key cylinder, when the engine key is inserted into the keycylinder, the ID code of the engine key is rendered corresponding to theID code of the immobilizer control unit, so that the engine key servesas the engine start key.

Further, according to another technical means of the invention, there isprovided a copy function in which the ID code of the allowance toolrecorded in the immobilizer control unit is written into another memberto cause the member to serve as an allowance tool.

Further, according to another technical means of the invention, there isprovided an allowance key copy function in which the ID code of theallowance key is written into another engine key to cause the engine keyto serve as an allowance key.

Further, according to another technical means of the invention, in theallowance key copy function of the immobilizer control unit, after theallowance key is inserted into a key cylinder, when another engine keyis inserted into the key cylinder, the ID code of the allowance key iswritten into the another engine key to cause it to serve as an allowancekey.

Further, according to another technical means of the invention, the IDcode of the engine start key registered by the start key registrationfunction can be recorded as an engine start key in an immobilizercontrol unit of another vehicle.

Further, according to another technical means of the invention, there isprovided a start key copy function in which the ID code of the enginestart key is written into another engine key to cause the engine key toserve as an engine start key.

Further, according to another technical means of the invention, in thestart key copy function of the immobilizer control unit, after theengine start key is inserted into a key cylinder, when another enginekey is inserted into the key cylinder, the ID code of the engine startkey is written into the another engine key to cause the engine key toserve as an engine start key.

Further, according to another technical means of the invention, there isprovided a delete function in which the ID code of the engine start keyrecorded in the immobilizer control unit is deleted from the immobilizercontrol unit.

Further, according to another technical means of the invention, there isprovided an engine start function with a special manipulation in whichwhen an engine key is inserted into a key cylinder and a specialmanipulation is performed, the starting of the engine is allowed.

Further, according to another technical means of the invention, there isprovided an initialization function in which an ID code memory portionof the immobilizer control unit is initialized.

Further, according to another technical means of the invention, when theallowance key is inserted into a key cylinder, the ID code of theallowance key is collated with the ID code recorded in the immobilizercontrol unit, and when the result of the collation is affirmative, acontrol mode for rendering the start key registration function operableis actuated.

Further, according to another technical means of the invention, when amaster key of the allowance key is inserted into the cylinder, a controlmode for rendering the allowance key copy function operable is actuated.

Further, according to another technical means of the invention, when amaster key of the engine start key is inserted into a key cylinder, acontrol mode for rendering the start key copy function operable isactuated.

Further, according to another technical means of the invention, avehicle to which the antitheft system is applied is a work machine suchas a backhoe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an antitheft device showing an embodimentof the invention.

FIG. 2 is a block diagram of the antitheft device of the sameembodiment.

FIG. 3 is a structural view of a display device, a main switch and thelike of the same embodiment.

FIG. 4 is a schematic view showing information (initial information)recorded in an EEPROM of each key of the same embodiment.

FIG. 5 is a schematic view showing information (initial information)recorded in an EEPROM of an immobilizer control unit of the sameembodiment.

FIG. 6 is a schematic view showing information recorded in a ROM of theimmobilizer control unit of the same embodiment.

FIG. 7 is an explanatory view showing the kind and role of each key ofthe same embodiment.

FIG. 8 is a flowchart showing the flow of a control mode of the sameembodiment.

FIG. 9( a) is a flowchart showing a registration operation procedure ofa first start key of the same embodiment.

FIG. 9( b) is a flowchart showing the registration operation procedureof the first start key of the same embodiment.

FIG. 10 is a schematic view showing a recording state of a ROM and thelike for explaining the registration operation procedure of the firststart key of the same embodiment.

FIG. 11 is a schematic view showing the recording state of the ROM andthe like for explaining the registration operation procedure of thefirst start key of the same embodiment.

FIG. 12 is a schematic view showing the recording state of the ROM andthe like for explaining the registration operation procedure of thefirst start key of the same embodiment.

FIG. 13( a) is a flowchart showing a registration operation procedure ofa second start key of the same embodiment.

FIG. 13( b) is a flowchart showing the registration operation procedureof the second start key of the same embodiment.

FIG. 14 is a schematic view showing the recording state of a ROM and thelike for explaining the registration operation procedure of the secondstart key of the same embodiment.

FIG. 15 is a schematic view showing the recording state of the ROM andthe like for explaining the registration operation procedure of thesecond start key of the same embodiment.

FIG. 16( a) is a flowchart showing a registration operation procedure ofa second allowance key of the same embodiment.

FIG. 16( b) is a flowchart showing the registration operation procedureof the second allowance key of the same embodiment.

FIG. 17 is a schematic view showing the recording state of the ROM andthe like for explaining the registration operation procedure of thesecond allowance key of the same embodiment.

FIG. 18 is a schematic view showing the recording state of the ROM andthe like for explaining the registration operation procedure of thesecond allowance key of the same embodiment.

FIG. 19( a) is a flowchart showing a copying operation procedure of asecond start key of the same embodiment.

FIG. 19( b) is a flowchart showing the copying operation process of thesecond start key of the same embodiment.

FIG. 20 is a schematic view showing a recording state of a ROM and thelike for explaining the copying operation procedure of the second startkey of the same embodiment.

FIG. 21 is a schematic view showing the recording state of the ROM andthe like for explaining the copying operation procedure of the secondstart key of the same embodiment.

FIG. 22( a) is a flowchart showing a copying operation procedure of asecond allowance key of the same embodiment.

FIG. 22( b) is a flowchart showing the copying operation procedure ofthe second allowance key of the same embodiment.

FIG. 23 is a schematic view showing a recording state of a ROM and thelike for explaining the copying operation procedure of the secondallowance key of the same embodiment.

FIG. 24 is a schematic view showing the recording state of the ROM andthe like for explaining the copying operation procedure of the secondallowance key of the same embodiment.

FIG. 25( a) is a flowchart showing a starting operation procedure of anengine of the same embodiment.

FIG. 25( b) is a flowchart showing the starting operation procedure ofthe engine of the same embodiment.

FIG. 26 is an explanatory view for explaining the operation procedureand effect of the same embodiment.

FIG. 27 is an explanatory view of a code input method by input means ofthe same embodiment.

FIG. 28 is a flowchart showing an operation procedure of use of a redkey in a vehicle resale mode of the same embodiment.

FIG. 29 is a schematic view showing a recording state of a ROM and thelike for explaining a vehicle resale operation procedure of the sameembodiment.

FIG. 30 is a schematic view showing the recording state of the ROM andthe like for explaining the vehicle resale operation procedure of thesame embodiment.

FIG. 31( a) is a flowchart showing a special manipulation operationprocedure in the vehicle resale mode of the same embodiment.

FIG. 31( b) is a flowchart showing the special manipulation operationprocedure in the vehicle resale mode of the same embodiment.

FIG. 32 is flowchart showing a keyless operation procedure in anemergency start mode of the same embodiment.

FIG. 33( a) is a flowchart showing a special manipulation operationprocedure in the emergency start mode of the same embodiment.

FIG. 33( b) is a flowchart showing the special manipulation operationprocedure in the emergency start mode of the same embodiment.

FIG. 34 is an explanatory view in which enquiries are made to amanufacturer about an engine starting code of the same embodiment.

FIG. 35 is a flowchart showing an operation of a personal computer of aservice center of the manufacturer of the same embodiment.

FIG. 36( a) is a flowchart showing a keyless operation procedure in aninitialization mode of the same embodiment.

FIG. 36( b) is a flowchart showing the keyless operation procedure inthe initialization mode of the same embodiment.

FIG. 37 is a schematic view showing a recording state of a ROM and thelike for explaining an initialization operation procedure of the sameembodiment.

FIG. 38 is a schematic view showing the recording state of the ROM andthe like for explaining the initialization operation procedure of thesame embodiment.

FIG. 39( a) is a flowchart showing a special manipulation operationprocedure in the initialization mode of the same embodiment.

FIG. 39( b) is a flowchart showing the special manipulation operationprocedure in the initialization mode of the same embodiment.

FIG. 40 is a flowchart showing another embodiment.

FIG. 41( a) is a flowchart showing another embodiment.

FIG. 41( b) is a flowchart showing the embodiment.

FIG. 42( a) is a flowchart of the same embodiment.

FIG. 42( b) is the flowchart of the same embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the invention will be described withreference to the drawings. FIGS. 1 to 3 show a structure of an antitheftdevice 1 provided in a work machine (vehicle) such as a backhoe which isa rotary work machine. In FIGS. 1 to 3, reference numeral 2 denotes amain switch (ignition switch) including a key cylinder 3 defining a keyhole 4 into which an engine key 5 is inserted for turning operation froman OFF position (OFF) to an ON position (ON) and a start position(START), and when the engine key 5 is inserted to set the main switch 2to the start position and the engine key 5 is released, the main switch2 is returned to the ON position by a force of a spring. Further, whenthe main switch 2 is set to the start position, a not-shown starter isconnected to a battery through the main switch 2.

A transponder chip 9 is embedded in a head part of the engine key 5. Asshown in FIG. 2, the transponder chip 9 of each engine key 5 includes aCPU 10, an EEPROM 11 and a transmission-reception unit 12, and an IDcode is recorded in the EEPROM 11 of the engine key 5.

An antenna 15, an amplifier 16, an immobilizer control unit 17 and adisplay device 18 are provided on a body of the work machine (vehicle).An engine start signal S is outputted from the immobilizer control unit17 to an engine control unit 19, whereby the engine control unit 19ignites an engine ignition device 20, and fuel is engine-injected from afuel injection device 21 to start the engine.

As shown in FIG. 2, the immobilizer control unit 17 includes animmobilizer CPU 23, an EEPROM 24, a ROM 25 and a RAM 26, and an ID codeis recorded in the immobilizer control unit 17.

The antenna 15 is provided to be externally fitted to the key cylinder3, and when the engine key 5 is inserted into the key cylinder 3 of themain switch 2 and is turned, the antenna 15 receives a signal of the IDcode transmitted from the transponder chip 9 of the engine key 5, theamplifier 16 amplifies the signal received by the antenna 15, and thesignal from the amplifier 16 is inputted to the immobilizer control unit17.

As shown in FIG. 3, a display device 18 includes a display part 29constructed of a liquid crystal or the like, and includes a first switch31, a second switch 32 and a third switch 33 of a push button type.Incidentally, the first switch 31, the second switch 32 and the thirdswitch 33 are used for, in addition to an operation to prevent theft, anoperation to blink a display light, and the like.

Further, a code (personal identification code) can be inputted by inputmeans of the first switch 31, the second switch 32 and the third switch33.

As shown in FIG. 27, in order to input a code by the input means, forexample, when the first switch 31 is pressed in a code input mode, acode 35 on a cursor 34 displayed on the display part 29 is changed, andeach time the first switch 31 is pressed, the number increases like “0,1, 2, . . . , 9”. When the first switch 31 is further pressed, thenumber returns to 0, and each time the first switch 31 is pressed, thecode 35 on the cursor 34 is changed from 0 to 9.

Further, each time the second switch 32 is pressed, the cursor 34 issequentially moved from the right to the left, and the digit of the code35 is changed, and when the second switch 32 is further pressed at theleftmost digit, the cursor is returned to the rightmost digit.

After the code 35 to be inputted is set by the first switch 31 and thesecond switch 32, when the third switch is pressed, the code 35 to beinputted is determined, and this code 35 is inputted to the immobilizercontrol unit 17.

Accordingly, the code 35 which can be expressed in a decimal number canbe inputted by the input means.

Alternatively, the input means may be arranged to input a code expressedin a hexadecimal number, or a code expressed in another number system.As a matter of course, in the case where the input code is expressed inthe hexadecimal number, each time the first switch 31 is pressed, thecode 35 on the cursor 34 is changed from 0 to F.

The main switch 2, the display device 18, the immobilizer control unit17 and the like are attached to an operation panel or the like in thevicinity of a driver's seat of a work machine.

As shown in FIGS. 4 to 7, each of the ID codes recorded in theimmobilizer control unit 17 and the engine key 5 includes acryptographic code for specifying the engine key 5, and a discriminationcode for distinguishing the kind of the engine key 5. In each of theengine keys 5, both the cryptographic code and the discrimination codeare recorded in the EEPROM 11 as shown in FIG. 4, while in theimmobilizer control unit 17, the cryptographic code is recorded in theEEPROM 24 as shown in FIG. 5, and the discrimination code is recorded inthe ROM 25 as shown in FIG. 6.

The engine keys 5 are distinguished by the discrimination code into afirst engine start key 5A for starting the engine (hereinafter referredto as a blue key for convenience), a second engine start key 5B forstarting the engine (hereinafter referred to as a yellow key forconvenience), a first allowance key 5C for allowing rewriting or writingof the ID code (hereinafter referred to as a red key for convenience),and a second allowance key 5D for allowing rewriting or writing of theID code (hereinafter referred to as a green key for convenience). Thesecond engine start keys (yellow keys) 5B are further distinguished intoa master key and a slave key by the discrimination code, and the secondallowance keys (green keys) 5D are also distinguished into a master keyand a slave key by the discrimination code.

Characters [a], [b], [c], [d], [e], [f], [g], [h], [i], [j], [k], [l],[m], [n], [o], [p], [q], [r], [s], [t], [u], [v], [w], and [x] shown inthe columns of the cryptographic code and the discrimination code shownin FIGS. 4, 5, 6, 10, 11, 12, 14, 15, 17, 18, 20, 21, 23 and 24 areone-digit or multi-digit numerals and stand for, for example, anumerical value of [123], and the numerals include also a numericalvalue of [0], [00], [01] or the like. Further, identical characters, forexample, [a] and [a] stand for an identical cryptographic code or anidentical discrimination code, while different characters, for example,[a] and [b] stand for different cryptographic codes or differentdiscrimination codes.

Incidentally, as shown in FIG. 6, the discrimination codes of [o to s]denote the blue keys 5A, the discrimination code of [t] denotes themaster key of the yellow key 5B, the discrimination code of [u] denotethe slave key of the yellow key 5B, the discrimination code of [v]denotes the red key 5C, the discrimination code of [w] denotes themaster key of the green key 5D, and the discrimination code of [x]denotes the slave key of the green key 5D.

As shown in FIG. 7, the blue key 5A is a key used for starting an engineof a specific work machine, that is, one specific work machine isprovided with only one blue key to be solely used for starting theengine of the specific work machine.

The yellow key 5B is a key used for starting the engine similarly to theblue key 5A, and one yellow key 5B, including the master key and theslave key, is used for starting engines of plural work machines.

The red key 5C is a key used for forming a new blue key 5A, a yellow key5B or a green key 5D from a commercially available engine key 5, butengines can not be started by this red key 5C.

The green key 5D is a key used for forming a new blue key 5A or a yellowkey 5B from a commercially available engine key 5 or the like similarlyto the red key 5C, but engines can not be started by this green key 5D.

The engine key 5 is the key which is inserted into the key hole of thekey cylinder 3 for turning operations of the main switch 2 from the OFFposition (OFF) to the ON position (ON) and the start position (START),and includes the blue key 5A, the yellow key 5B, the red key 5C and thegreen key 5D.

Incidentally, in order to distinguish the respective keys, for example,as shown in FIG. 7, the head part of the blue key 5A is colored inblack, and no sticker is stuck on the head part. The head part of themaster key of the yellow key 5B is colored in black, and a yellowsticker is stuck on the head part. The head part of the slave key of theyellow key 5B is colored in black, and a yellow sticker is stuck on thehead part. The head part of the red key 5C is colored in red, and nosticker is stuck on the head part. The head part of the master key ofthe green key 5D is colored in black, and a green sticker is stuck onthe head part. The head part of the slave key of the green key 5D iscolored in black, and a green sticker is stuck on the head part.

By the control of the immobilizer control unit 17 (or the CPU 10 of theengine key 5), the capability or incapability of rewriting of ID codesrecorded in the respective keys 5 and the immobilizer control unit 17 isset as follows.

As shown in FIG. 4, both the cryptographic code and the discriminationcode recorded in the blue key 5A can be rewritten. Both thecryptographic code and the discrimination code recorded in the masterkey of the yellow key 5B can not be rewritten, while both thecryptographic code and the discrimination code recorded in the slave keyof the yellow key 5B can be rewritten. Both the cryptographic code andthe discrimination code recorded in the red key 5C can not be rewritten.Both the cryptographic code and the discrimination code recorded in themaster key of the green key 5D can not be rewritten, while both thecryptographic code and the discrimination code recorded in the slave keyof the green key 5D can be rewritten.

As shown in FIG. 5, the cryptographic code of the blue key 5A recordedin the immobilizer control unit 17 can be rewritten. With respect to thecryptographic code of the yellow key 5B recorded in the immobilizercontrol unit 17, both the master key and the slave key can be rewritten.The cryptographic code of the red key 5C recorded in the immobilizercontrol unit 17 can not be rewritten in principle. However, only in anexceptional case, for example, when recording of the EEPROM 24 of theimmobilizer control unit 17 is returned to an initial state, it can berewritten. With respect to the cryptographic code of the green key 5Drecorded in the immobilizer control unit 17, both the master key and theslave key can be rewritten.

As shown in FIG. 6, the discrimination codes recorded in the ROM 25 ofthe immobilizer control unit 17 can not be rewritten.

The immobilizer control unit 17 includes, in addition to an engine startallowance function to allow the starting of the engine, a start keyregistration function, an allowance key registration function, a startkey copy function, and an allowance key copy function, which will bedescribed below.

The engine start allowance function determines whether or not thestarting of the engine should be allowed when the blue key 5A or theyellow key 5B is inserted into the key cylinder 3 to perform the enginestarting operation, so that theft with an invalid key can be prevented.The ID code of the blue key 5A or the yellow key 5B is collated with theID code recorded in the immobilizer control unit 17. When the result ofthe collation is affirmative, the starting of the engine with the bluekey 5A or the yellow key 5B is allowed, an engine signal S is outputtedfrom the immobilizer control unit 17 to the engine control unit 19, andthe engine is started. When the result of the collation is negative, theengine start signal S is not outputted from the immobilizer control unit17 to the engine control unit 19, and the starting of the engine isprevented.

The control modes of the immobilizer control unit 17 are changed asfollows. When the engine key 5 is inserted into the key cylinder 3 withthe third switch 33 of the display device 18 pressed, and the mainswitch 2 is turned from the OFF position (OFF) to the ON position (ON),control modes for preventing theft starts, as shown in FIG. 8, and “eachkey registration mode” of a main menu initially starts. Each time thethird switch 33 is pressed, the control mode of the main menu issequentially changed from “each key registration mode” to “each key copymode”, “vehicle resale mode”, “emergency start mode”, and“initialization mode”, and by further pressing the third switch 33, themode is returned to “each key registration mode”, and hereafter, eachtime the third switch 33 is pressed, the changeover of the control modeof the main menu is repeated.

When the second switch 32 is pressed in the “each key registrationmode”, the changeover of control modes of submenu starts, and each timethe second switch 32 is pressed, the control mode of the submenu issequentially changed to “blue key registration”, “yellow keyregistration” and “green key registration”, and each time the secondswitch 32 is pressed, the same changeover of the control mode of thesubmenu is repeated.

When the second switch 32 is pressed in the “each key copy mode”, thechangeover of control modes of submenu starts, and each time the secondswitch 32 is pressed, the control mode of the submenu is sequentiallychanged to “yellow key copy” and “green key copy”, and each time thesecond switch 32 is pressed, the same changeover of the control mode ofthe submenu is repeated.

When the second switch 32 is pressed in the “vehicle resale mode”, thechangeover of control modes of submenu starts, and each time the secondswitch 32 is pressed, the control mode of the submenu is sequentiallychanged to “red key use” and “special manipulation”, and each time thesecond switch 32 is pressed, the same changeover of the control mode ofthe submenu is repeated.

When the second switch 32 is pressed in the “emergency start mode”, thechangeover of control modes of submenu starts, and each time the secondswitch 32 is pressed, the control mode of the submenu is sequentiallychanged to “special manipulation” and “keyless”, and each time thesecond switch 32 is pressed, the same changeover of the control mode ofthe submenu is repeated.

When the second switch 32 is pressed in the “initialization mode”, thechangeover of control modes of submenu starts, and each time the secondswitch 32 is pressed, the control mode of the submenu is sequentiallychanged to “special manipulation” and “keyless”, and each time thesecond switch 32 is pressed, the same changeover of the control mode ofthe submenu is repeated.

In the control mode of “blue key registration” of “each key registrationmode”, the blue key 5A is formed from a commercially available enginekey 5 through the start key registration function provided in theimmobilizer control unit 17. In this start key registration function,the ID code of the red key 5C or the green key 5D is collated with theID code recorded in the immobilizer control unit 17, and when the resultof the collation is affirmative, the ID code of the engine key 5 isrendered corresponding to the ID code of the immobilizer control unit 17so that the engine key 5 serves as the blue key 5A.

More specifically, in the control mode of “blue key registration” of“each key registration mode”, when the red key 5C or the green key 5D isinserted into the key cylinder 3, and then the engine key 5 is insertedinto the key cylinder 3, the memory area of the EEPROM 24 of theimmobilizer control unit 17 corresponding to the discrimination code ofthe blue key 5A is cleared, and the cryptographic code of the engine key5 is written into this area, while the discrimination code of the bluekey recorded in the ROM 25 of the immobilizer control unit 17 is writteninto the engine key 5, so that identical pairs of cryptographic code anddiscrimination code are recorded in the engine key 5 and the immobilizercontroller 17. As a result, the ID code of the engine key 5 is renderedcorresponding to the ID code of the immobilizer control unit 17, so thatthe engine key 5 serves as the blue key 5A. Further, at this time,overwriting of the discrimination code of the registered blue key 5A isrendered impossible, and registration of the cryptographic code of theblue key 5A is rendered impossible so that this blue key 5A can not beregistered as the blue key into an immobilizer control unit of anotherwork machine.

In the control mode of “yellow key registration” of “each keyregistration mode”, the yellow key 5B having a function as an enginestart key is formed from an engine key 5 (yellow key 5B) which does notserve as the engine start key through the start key registrationfunction provided in the immobilizer control unit 17. In this start keyregistration function, the ID code of the red key 5C or the green key 5Dis collated with the ID code recorded in the immobilizer control unit17, and when the result of the collation is affirmative, the ID code ofthe engine key 5 is rendered corresponding to the ID code of theimmobilizer control unit 17 so that the engine key 5 serves as theyellow key 5B.

More specifically, in the control mode of “yellow key registration” of“each key registration mode”, when the red key 5C or the green key 5D isinserted into the key cylinder 3, and then the engine key 5 (the yellowkey 5B in which the cryptographic code and the discrimination code arerecorded, but which does not serve as the engine start key) is insertedinto the key cylinder 3, the cryptographic code of this engine key 5 iswritten into the memory area of the EEPROM 24 of the immobilizer controlunit 17 corresponding to the discrimination code of the yellow key 5B,so that identical pairs of cryptographic code and discrimination codeare recorded in the engine key 5 and the immobilizer control unit 17. Asa result, the ID code of the engine key 5 is rendered corresponding tothe ID code of the immobilizer control unit 17, so that the engine key 5serves as the yellow key 5B. Further, at this time, in order that theregistered yellow key 5B can be registered as the yellow key into animmobilizer control unit of another work machine, the registration ofthe cryptographic code of the yellow key 5B is not rendered impossible,but is made to remain possible.

In the control mode of “green key registration” of “each keyregistration mode”, the green key 5D having a function as an allowancekey is formed from an engine key 5 (green key 5D) which does not serveas the allowance key through the allowance key registration functionprovided in the immobilizer control unit 17. In this allowance keyregistration function, the ID code of the red key 5C is collated withthe ID code recorded in the immobilizer control unit 17, and when theresult of the collation is affirmative, the ID code of the engine key 5is rendered corresponding to the ID code of the immobilizer control unit17 so that the engine key 5 serves as the green key 5D.

More specifically, in the control mode of “green key registration” of“each key registration mode”, when the red key 5C is inserted into thekey cylinder 3, and then the engine key 5 (green key 5D in which thecryptographic code and the discrimination code are recorded, but whichdoes not function as the allowance key) is inserted into the keycylinder 3, the cryptographic code of this engine key 5 is written intothe memory area of the EEPROM 24 of the immobilizer control unit 17corresponding to the discrimination code of the green key 5D, so thatidentical pairs of cryptographic code and discrimination code arerecorded in the engine key 5 and the immobilizer control unit 17. As aresult, the ID code of the engine key 5 is rendered corresponding to theID code of the immobilizer control unit 17, so that the engine key 5serves as the green key 5D. Further, at this time, in order that theregistered green key 5D can be registered as the green key into animmobilizer control unit of another work machine, the registration ofthe cryptographic code of the green key 5D is not rendered impossible,but is made to remain possible.

In the control mode of “yellow key copy” of “each key copy mode”, theslave key of the yellow key 5B is formed from a commercially availableengine key 5 (or unregistered blue key 5A) with using the master key ofthe yellow key 5B through the start key copy function provided in theimmobilizer control unit 17. In the start key copy function, the ID codeof the master key of the yellow key 5B is written into another enginekey 5 so that the engine key serves as an engine start key.

More specifically, in the control mode of “yellow key copy” of “each keycopy mode”, when the master key of the yellow key 5B is inserted intothe key cylinder 3, the ID code (only the cryptographic code) of themaster key is written into the RAM 26 of the immobilizer control unit17, and then, when another engine key 5 is inserted into the keycylinder 3, the cryptographic code of the master key written in theimmobilizer control unit 17 and the discrimination code denoting theslave key of the yellow key 5B are written into the EEPROM 11 of theengine key 5. As a result, identical pairs of cryptographic code anddiscrimination code are recorded in the engine key 5 and the immobilizercontrol unit 17, whereby the ID code of the engine key 5 is renderedcorresponding to the ID code of the immobilizer control unit 17, and themaster key of the yellow key 5B is copied into the engine key 5 as theslave key of the yellow key 5B.

In the control mode of “green key copy” of “each key copy mode”, theslave key of the green key 5D is formed from a commercially availableengine key 5 (or unregistered blue key 5A) with using the master key ofthe green key 5D through the allowance key copy function provided in theimmobilizer control unit 17. In the allowance key copy function, the IDcode of the master key of the green key 5D is written into anotherengine key 5 so that the engine key serves as an allowance key.

More specifically, in the control mode of “green key copy” of “each keycopy mode”, when the master key of the green key 5D is inserted into thekey cylinder 3, the ID code (only the cryptographic code) of the masterkey is written into the RAM 26 of the immobilizer control unit 17, andthen, when another engine key 5 is inserted into the key cylinder 3, thecryptographic code of the master key written in the immobilizer controlunit 17 and the discrimination code denoting the slave key of the greenkey 5D are written into the EEPROM 11 of the engine key 5. As a result,pairs of identical cryptographic codes and discrimination codes arerecorded in the engine key 5 and the immobilizer control unit 17, sothat the ID code of the engine key 5 is rendered corresponding to the IDcode of the immobilizer control unit 17, and the master key of the greenkey 5D is copied into the engine key 5 as the slave key of the green key5D.

In the control mode of “vehicle resale mode”, the ID code of the yellowkey 5B recorded in the EEPROM 24 of the immobilizer control unit 17 isdeleted from the immobilizer control unit 24 for preventing the enginefrom being started by the yellow key 5B before the resale, since if, forexample, a work machine whose engine can be started by plural yellowkeys 5B is resold, the engine of the work machine after the resale canbe started by the plural yellow keys 5B recorded in the EEPROM 24 of theimmobilizer control unit 17 before the resale.

Further, in the control mode of “vehicle resale mode”, the ID code ofthe green key 5D recorded in the EEPROM 24 of the immobilizer controlunit 17 is also deleted from the immobilizer control unit 17, since ifthe ID code of the green key 5D recorded in the EEPROM 24 of theimmobilizer control unit 17 before the resale remains recorded in theEEPROM 24 of the immobilizer control unit 17 after the resale, acommercially available engine key 5 can be registered as the enginestart key 5A, 5B with using the green key 5D before the resale. Thecontrol mode of “vehicle resale mode” is performed by a delete functionprovided in the immobilizer control unit 17.

This delete function includes a delete function using a red key in whichwhen a valid red key 5C is inserted into the key cylinder 3, the ID codeof the yellow key 5B or the green key 5D recorded in the EEPROM 24 ofthe immobilizer control unit 17 is deleted from the EEPROM 24 of theimmobilizer control unit 17, and a delete function using a specialmanipulation in which when the engine key 5 is inserted into the keycylinder 3 and a special manipulation is performed, the ID code of theyellow key 5B or the green key 5D recorded in the EEPROM 24 of theimmobilizer control unit 17 is deleted from the EEPROM 24 of theimmobilizer control unit 17.

In the delete function using the red key in the control mode of “red keyuse” of “vehicle resale mode”, after the red key 5C is inserted into thekey cylinder 3, the discrimination code of the red key 5C is collatedwith the discrimination code of the immobilizer control unit 17corresponding thereto, and the cryptographic code of the red key 5C iscollated with the cryptographic code of the immobilizer control unit 17corresponding thereto. When the results of respective collations areaffirmative, the cryptographic code of the yellow key 5B recorded in theEEPROM 24 of the immobilizer control unit 17 is deleted from the EEPROM24 of the immobilizer control unit 17, and the cryptographic code of thegreen key 5D recorded in the EEPROM 24 of the immobilizer control unit17 is deleted from the EEPROM 24 of the immobilizer control unit 17.

In the delete function using the special manipulation in the controlmode of “special manipulation” of “vehicle resale mode”, after theignition switch 2 is ON-OFF rotated by the engine key 5, the immobilizercontrol unit 17 receives the ON-OFF rotation signal of the key cylinder3, the immobilizer CPU 23 of the immobilizer control unit 17 counts thenumber of times of ON-OFF rotation of the ignition switch 2, that is,how many times the ignition switch 2 is rotated from the OFF position tothe ON position by the engine key 5. When the number of times of ON-OFFrotation of the ignition switch 2 after the lapse of a predeterminedperiod of time from the start of the ON-OFF rotation coincides with apredetermined number of times, the cryptographic code of the yellow key5B recorded in the EEPROM 24 of the immobilizer control unit 17 isdeleted from the EEPROM 24 of the immobilizer control unit 17, and thecryptographic code of the green key 5D recorded in the EEPROM 24 of theimmobilizer control unit 17 is deleted from the EEPROM 24 of theimmobilizer control unit 17.

Incidentally, the engine key 5 used in the special manipulation may beany key as long as the ignition switch 2 can be rotated from the OFFposition to the ON position.

The control mode of “keyless” of “emergency start mode” is for enablingthe starting of the engine especially in the case where, for example,the blue key 5A and the yellow key 5B to start the engine are lost, andis performed by the engine start function through code input provided inthe immobilizer control unit 17.

In the engine start function through the code input, when the codeinputted by the input means coincides with the engine starting coderecorded in the ROM 25 of the immobilizer control unit 17, the startingof the engine is allowed.

More specifically, in the control mode of “keyless” of “emergency startmode”, the conversion function provided in the immobilizer control unit17 is actuated for converting the engine starting code recorded in theimmobilizer control unit 17 into a vehicle registration number (dummyengine starting code, conversion code) for specifying the work machine(antitheft device 1) which is displayed by the display means 19 so thata code can be inputted by the input means. In the case where the inputcode inputted by the input means coincides with the engine startingcode, the engine starting is allowed.

The control mode of “special manipulation” of “emergency start mode” is,similarly to the control mode of “keyless” of “emergency start mode”,for enabling the engine starting especially in the case where the bluekey 5A and the yellow key 5B to start the engine are lost, and isperformed by the engine start function through the special manipulationprovided in the immobilizer control unit 17.

The engine start function through the special manipulation allows thestarting of the engine when the engine key 5 is inserted into the keycylinder 3 and the special manipulation is performed.

More specifically, in the control mode of “special manipulation” of“emergency start mode”, when the ignition switch 2 is ON-OFF rotated bythe engine key 5, the immobilizer control unit 17 receives the ON-OFFrotation signal of the key cylinder 3, and the immobilizer CPU 23 of theimmobilizer control unit 17 counts how many times the ignition switch 2is rotated from the OFF position to the ON position by the engine key 5,that is, the number of times of ON-OFF rotation of the ignition switch2. When the number of times of ON-OFF rotation of the ignition switch 2after the lapse of a predetermined period of time from the start of theON-OFF rotation is coincides with a predetermined number of times, theengine starting is allowed.

Incidentally, the engine key 5 used for this special manipulation may beany key as long as it can be fitted in the key hole of the key cylinder3 and can rotate the ignition switch 2.

The control mode of “initialization mode” is for initializing the IDcode recorded in the immobilizer control unit 17 of the work machine inthe case where the yellow key 5B is recorded in plural immobilizercontrol units 17, or the plural blue keys 5A are recorded in one workmachine, and when it becomes unclear which engine start key 5A, 5Bcorresponds to which work machine, and this mode is performed by theinitialization function provided in the immobilizer control unit 17.

This initialization function includes an initialization function throughcode input in which the recording portion of the ID code of theimmobilizer control unit 17 is initialized when a code inputted by theinput means coincides with an initialization code to initialize the IDcode recorded in the immobilizer control unit 17, and an initializationfunction through a special manipulation in which the recording portionof the ID code of the immobilizer control unit 17 is initialized when akey (engine key 5) capable of rotating the ignition switch 2 from theOFF position to the ON position is inserted into the key cylinder 3 andthe special manipulation is performed.

In the initialization function through the code input in the controlmode of “keyless” of “initialization mode”, the conversion functionprovided in the immobilizer control unit 17 is actuated for convertingthe initialization code recorded in the immobilizer control unit 17 intoa vehicle registration number (dummy initialization code, conversioncode) for specifying the work machine which is displayed on the displaymeans 19 so that a code can be inputted by the input means. When theinput code inputted by the input means coincides with the initializationcode, the engine key 5 is allowed to be recorded as the red key 5C intothe immobilizer control unit 17, and after the engine key 5 is recordedas the red key 5C (the cryptographic code of the engine key 5 is writteninto the EEPROM 24 of the immobilizer control unit 17, and thediscrimination code of the immobilizer control unit 17 corresponding tothe red key 5C is written into the EEPROM 11 of the engine key 5), thecryptographic codes (blue key, yellow key, green key) other than the redkey 5C recorded in the immobilizer control unit 17 are cleared.

In the initialization function through the special manipulation in thecontrol mode of “keyless” of “initialization mode”, when the ignitionswitch 2 is ON-OFF rotated by the engine key 5, the immobilizer controlunit 17 receives the ON-OFF rotation signal of the key cylinder 3, andthe immobilizer CPU 23 of the immobilizer control unit 17 counts howmany times the ignition switch 2 is rotated by the engine key 5 from theOFF position to the ON position, that is, the number of times of ON-OFFrotation of the ignition switch 2. When the number of times of ON-OFFrotation of the ignition switch 2 after the lapse of a predeterminedtime from the start of the ON-OFF rotation coincides with apredetermined number of times, the engine key 5 is allowed to berecorded as the red key 5C into the immobilizer control unit 17, andafter the engine key 5 is recorded as the red key 5C (the cryptographiccode of the engine key 5 is written into the EEPROM 24 of theimmobilizer control unit 17, and the discrimination code of theimmobilizer control unit 17 corresponding to the red key 5C is writteninto the EEPROM 11 of the engine key 5), the cryptographic codes (bluekey, yellow key, green key) other than the red key 5C recorded in theimmobilizer control unit 17 are cleared.

Incidentally, the engine key 5 used for this special manipulation may beany key as long as it can be fitted in the key hole of the key cylinder3 and can rotate the ignition switch 2.

Further, the immobilizer control unit 17 controls the display part 29,and the display part 29 sequentially variably displays the operation toperform the start key registration function, and each time the operationis performed, the operation to be performed next is sequentiallyvariably displayed. Further, the display part 29 is controlled tosequentially variably display the control mode of the immobilizercontrol unit 17.

When a work machine such as a backhoe is sold, a dealer sells one workmachine with four keys in total, as marked by double circles in FIG. 4,that is, one blue key 5A, a master key of one yellow key 5B, one red key5C and a master key of one green key 5D to a user (a rental company ofthe work machine, a personal user).

At this time, as shown in FIG. 4, only the cryptographic code isrecorded in the blue key 5A, and the discrimination code is not recordedtherein, and the memory area of the discrimination code remains in ablank state. Accordingly, in this state, the blue key 5A does not havethe function of the engine start key. The cryptographic code and thediscrimination code are recorded in the yellow key 5B, the red key 5Cand the green key 5D.

On the other hand, in the EEPROM 24 of the immobilizer control unit 17of the work machine, only the cryptographic code of the red key 5C isrecorded, and the memory areas of the cryptographic codes of the otherkeys remain in blank states. Further, in the ROM 25 of the immobilizercontrol unit 17, the discrimination codes of the blue keys 5A of Nos. 1to 5, the discrimination code of the master key of the yellow key 5B,the discrimination code of the slave key of the yellow key 5B, thediscrimination code of the red key 5C, the discrimination code of themaster key of the green key 5D, and the discrimination code of the slavekey of the green key 5D are recorded.

Next, the operation procedure of the control mode of “blue keyregistration” in “each key registration mode” will be described withreference to flowcharts of FIG. 9( a) and 9(b).

In step 1 of the control mode of “blue key registration” of “each keyregistration mode”, the display part 29 displays “blue key registration”of “each key registration mode” and ‘Please insert red key or greenkey’, and then, the procedure advances to step 2.

In the step 2, it is judged whether or not the engine key 5 is insertedinto the key cylinder 3. When it is judged that the engine key 5 isinserted, the procedure advances to step 3, and when it is judged thatthe engine key 5 is not inserted, the procedure returns to step 1.

Accordingly, when the control mode of “blue key registration” starts,the display of “blue key registration” of “each key registration mode”and ‘Please insert red key 5C or green key 5D’ on the display part 29continues until the engine key 5 is inserted into the key cylinder 3 tourge the insertion of the red key 5C or the green key 5D into the keycylinder 3.

In the step 3, it is judged whether or not the discrimination code ofthe engine key 5 inserted into the key cylinder 3 is identical with thediscrimination code of the red key 5C or the green key 5D. When it isidentical with the discrimination code of the red key 5C or the greenkey 5D, the procedure advances to step 5, and when it is not identicalwith the discrimination code of the red key 5C or the green key 5D, theprocedure advances to step 4 with displaying ‘Key does not coincide’ onthe display part 29 for a predetermined period of time (severalseconds), and the procedure returns to step 1.

In the step 5, it is judged whether or not the cryptographic code of theengine key 5 inserted into the key cylinder 3 is identical with thecryptographic code recorded in the immobilizer control unit 17. When thecryptographic codes are identical, the procedure advances to step 6, andwhen the cryptographic codes are not identical, the procedure advancesto step 4 with displaying ‘Key does not coincide’ on the display part29, and the procedure returns to step 1.

Accordingly, when the engine key 5 other than the registered red key 5Cor the green key 5D is inserted into the key cylinder 3, after it isnotified that the key different from the red key 5C or the green key 5Dhas been inserted into the key cylinder 3 by displaying ‘Key does notcoincide’ on the display part 29, the insertion of the red key 5C or thegreen key 5D into the key cylinder 3 is urged again.

In the step 5, when the cryptographic codes are judged to be identical,the process advances to step 6 in which the memory area of thecryptographic code, corresponding to the blue key 5A, of the EEPROM 24of the immobilizer control unit 17 is cleared (see FIG. 11), and then,the procedure advances to step 7. In the step 7, ‘Please insert blue key5A’ is displayed on the display part 29 (until a new key is insertedinto key cylinder 3), and the procedure advances to step 8.

In the step 8, it is judged whether or not the engine key 5 insertedinto the key cylinder 3 can be registered. In this judgment, only whenthe cryptographic code is recorded in the inserted engine key 5, and thememory area of the discrimination code of the engine key 5 is blank orthe discrimination code of the blue key is recorded in the memory areaof the discrimination code, the engine key is judged to be registrable,and the procedure advances to step 10. When the engine key 5 insertedinto the key cylinder 3 contains a discrimination code other than thatof the blue key 5A, that is, the discrimination code of the master keyof the yellow key 5B, the discrimination code of the slave key of theyellow key 5B, the discrimination code of the master key of the greenkey 5D, or the discrimination code of the slave of the green key 5D, orthe engine key is a blank key (engine key 5 in which the cryptographiccode is not recorded), the engine key is judged to be unregistrable, andthe procedure advances to step 9. In the step 9, ‘This key can not beregistered’ is displayed on the display part 29, and the procedurereturns to step 8.

Accordingly, only the engine key 5 in which the cryptographic code isrecorded and any discrimination code other than the blue key 5A is notrecorded can be registered as the blue key, and the engine key 5 otherthan this can not be registered.

In the step 10, the cryptographic code of the engine key 5 inserted intothe key cylinder 3 is written into the memory area, corresponding to theblue key, of the EEPROM 24, and in step 11, the discrimination code ofthe blue key is written into the EEPROM 11 of the inserted engine key 5.In step 12, overwriting of the discrimination code of the registeredengine key 5 (blue key 5A) is rendered impossible, registration of thecryptographic code is rendered impossible, and then, the procedureadvances to step 13.

Accordingly, among the engine keys 5, with respect to the engine key 5in which only the cryptographic code is recorded and the discriminationcode is not recorded, or the engine key 5 (unregistered blue key 5A) inwhich the cryptographic code is recorded and the discrimination code ofthe blue key is recorded, the ID code of the engine key 5 corresponds tothe ID code of the immobilizer control unit 17 so that the blue key isregistered to serve as the engine start key, a new blue key 5A isformed, and the engine can be started by this blue key 5A. In thisoperation, since the overwriting of the discrimination code of the bluekey 5A is rendered impossible, this blue key 5A can not be changed tothe yellow key 5B or the other key after this operation. Further, sincethe registration of the cryptographic code of the blue key 5A isrendered impossible, this blue key 5A can not be registered as the bluekey in the immobilizer control unit 17 of another work machine afterthis operation, and accordingly, this blue key 5A can be used only forthe starting of the engine of the work machine corresponding to thiskey.

In the step 12, the overwriting of the discrimination code of theregistered engine key 5 (blue key 5A) is rendered impossible, and theregistration of the cryptographic code is rendered impossible.Alternatively, in the step 12, the overwriting and the registration ofthe ID code (cryptographic code and discrimination code) of theregistered engine key 5 (blue key 5A) may be rendered impossible.

In step 13, it is judged whether or not further engine key 5 is to beregistered as the blue key 5A, and when it is judged that the engine key5 is to be registered, the procedure returns to step 7, and theregistration operation of the next engine key 5 is performed. Thejudgment of whether or not the registration is to be performed is madeaccording to, for example, whether or not the first switch 31 isoperated to be ON within a predetermined period of time. When the firstswitch 31 is operated to be ON, it is judged that the engine key 5 isregistered as the blue key, and the procedure returns to step 7, andwhen the first switch 31 is not operated to be ON within thepredetermined period of time, it is judged that the engine key 5 is notregistered, and the registration operation of the blue key 5A ends.Accordingly, the registration of the blue key can be continuouslyperformed with respect to plural engine keys 5.

Accordingly, for example, as shown in the left table of FIG. 10, in thecase where the cryptographic code is recorded in the EEPROM 24 of theimmobilizer control unit 17, for registering a newly purchased enginekey 5 with a cryptographic code of [i] and an engine key 5 with acryptographic code of [j] as shown in the right table of FIG. 10 as bluekeys, the memory area of the cryptographic code, corresponding to theblue key, of the EEPROM 24 of the immobilizer control unit 17 is oncecleared, as shown in FIG. 11 (step 6).

Thereafter, as shown in the left table of FIG. 12, the cryptographiccode of [i] and the cryptographic code of [j] are recorded in the twomemory areas of the cryptographic code, corresponding to the blue keys5A, of the EEPROM 24 of the immobilizer control unit 17, and as shown inthe right table of FIG. 12, the discrimination code of [o] and thediscrimination code of [p] are recorded in the memory areas of thediscrimination codes of the EEPROMs 11 of the two engine keys 5. As aresult, two blue keys 5A are formed, and the engine can be started bythese keys.

Next, the operation procedure of the control mode of “yellow keyregistration” in “each key registration mode” will be described withreference to flowcharts of FIG. 13( a) and FIG. 13( b).

In step 21 of the control mode of “yellow key registration” of “each keyregistration mode”, the display part 29 displays “yellow keyregistration” of “each key registration mode” and ‘Please insert red keyor green key’, and then, the procedure advances to step 22.

In the step 22, it is judged whether or not the engine key 5 is insertedinto the key cylinder 3. When it is judged that the engine key 5 isinserted, the procedure advances to step 23, and when it is judged thatthe engine key 5 is not inserted, the procedure returns to step 21.

Accordingly, when the control mode of “yellow key registration” starts,the display of “yellow key registration” of “each key registration mode”and ‘Please insert red key 5C or green key 5D’ on the display part 29continues until the engine key 5 is inserted into the key cylinder 3 tourge the insertion of the red key 5C or the green key 5D into the keycylinder 3.

In the step 23, it is judged whether or not the discrimination code ofthe engine key 5 inserted into the key cylinder 3 is identical with thediscrimination code of the red key 5C or the green key 5D. When it isidentical with the discrimination code of the red key 5C or the greenkey 5D, the procedure advances to step 25, and when it is not identicalwith the discrimination code of the red key 5C or the green key 5D, theprocedure advances to step 24 with displaying ‘Key does not coincide’ onthe display part 29 for a predetermined period of time (severalseconds), and the procedure returns to step 21.

In the step 25, it is judged whether or not the cryptographic code ofthe engine key 5 inserted into the key cylinder 3 is identical with thecryptographic code recorded in the immobilizer control unit 17. When thecryptographic codes are identical, the procedure advances to step 26,and when the cryptographic codes are not identical, the procedureadvances to step 24 with displaying ‘Key does not coincide’ on thedisplay part 29, and the procedure returns to step 21.

Accordingly, when the engine key 5 other than the registered red key 5Cor the green key 5D is inserted into the key cylinder 3, after it isnotified that the erroneous key different from the red key 5C or thegreen key 5D has been inserted into the key cylinder 3 by displaying‘Key does not coincide’ on the display part 29, the insertion of the redkey 5C or the green key 5D into the key cylinder 3 is urged again.

In the step 25, when the cryptographic codes are judged to be identical,the procedure advances to step 26, and in the step 26, ‘Please insertyellow key’ is displayed on the display part 29 (until a new key isinserted into the key cylinder 3), and the procedure advances to step27.

In the step 27, it is judged whether or not the engine key 5 insertedinto the key cylinder 3 can be registered. In this step, when theinserted engine key 5 is the master key or the slave key of the yellowkey, that is, the cryptographic code is recorded in the inserted enginekey 5, and the discrimination code of the master key of the yellow keyor the discrimination code of the slave key of the yellow key 5B isrecorded in the memory area of the discrimination code of the engine key5, the key is judged to be registrable, and the procedure advances tostep 29. In the case where a discrimination code other than thediscrimination code of the master key or the slave key of the yellow keyis recorded in the engine key 5 inserted into the key cylinder 3, in thecase where the discrimination code is not recorded, or in the case wherethe cryptographic code is not recorded, the key is judged to beunregistrable, and the procedure advances to step 28. In the step 28,‘This key can not be registered’ is displayed on the display part 29,and the procedure returns to step 26.

Accordingly, in the case where the cryptographic code is recorded in theinserted engine key 5, and the discrimination code of the master key orthe slave key of the yellow key is recorded in the memory area of thediscrimination code of the engine key 5, the engine key 5 can beregistered as the yellow key 5B (master key and slave key), and anengine key 5 other than this can not be registered.

In the step 29, the cryptographic code of the engine key 5 inserted intothe key cylinder 3 is written into the memory area, corresponding to themaster key of the yellow key 5B, in the EEPROM 24 of the immobilizercontrol unit 17, and at this time, the same cryptographic code issimultaneously written into the memory area, corresponding to the slavekey of the yellow key, in the EEPROM 24, and the registration operationof the yellow key ends.

Accordingly, among the engine keys 5, with respect to the key in whichthe cryptographic code is recorded and the discrimination code of themaster key or the slave key of the yellow key is recorded, the ID codeof the engine key 5 corresponds to the ID code of the immobilizercontrol unit 17 so that the yellow key (master key and slave key) isregistered to serve as the engine start key, and the engine can bestarted by this master key of the yellow key 5B or slave key of theyellow key 5B.

Accordingly, for example, as shown in the left table of FIG. 14, in thecase where the memory areas of the cryptographic code, corresponding tothe master key and the slave key of the yellow key, of the EEPROM 24 ofthe immobilizer control unit 17 are blank, and the yellow key 5B is notregistered, the master key or the slave key of the yellow key in whichthe cryptographic code of [f] is recorded, as shown in the right tableof FIG. 14, enables the cryptographic code of [f] to be recorded intothe memory area corresponding to the master key of the yellow key andthe memory area corresponding to the slave key of the yellow key of theEEPROM 24 of the immobilizer control unit 17, as shown in the left tableof FIG. 15, whereby the yellow key 5B is registered, and the engine canbe started by the master key of the yellow key 5B or the slave key ofthe yellow key 5B.

Further, in the registration operation of the yellow key, differentlyfrom the registration operation of the blue key, since the registrationof the cryptographic code is not rendered impossible, the registeredyellow key 5B can also be registered as the yellow key 5B into theimmobilizer control unit 17 of another work machine.

Incidentally, in the operation procedure of the control mode of “yellowkey registration”, when one of the master key of the yellow key 5B andthe slave key of the yellow key 5B is registered, the cryptographic codeof the yellow key 5B is written into the memory area, corresponding tothe master key of the yellow key 5B, in the EEPROM 24 of the immobilizercontrol unit 17, and simultaneously, the identical cryptographic code iswritten into the memory area corresponding to the slave key of theyellow key 5B, so that both the master key of the yellow key 5B and theslave key of the yellow key 5B are registered. Alternatively, the memoryarea of the cryptographic code, corresponding to the master key of theyellow key 5B, in the EEPROM 24 may be made in common with the memoryarea of the cryptographic code corresponding to the slave key of theyellow key 5B, so that the registration operation of one of the masterkey of the yellow key 5B and the slave key of the yellow key 5B canregister both of the master key of the yellow key 5B and the slave keyof the yellow key 5B. Alternatively, the master key of the yellow key 5Band the slave key of the yellow key 5B may be separately registered.

Next, the operation procedure of the control mode of “green keyregistration” in “each key registration mode” will be described withreference to flowcharts of FIG. 16( a) and FIG. 16( b).

In step 41 of the control mode of “green key registration” of “each keyregistration mode”, the display part 29 displays “green keyregistration” of “each key registration mode” and ‘Please insert redkey’, and the procedure advances to step 42.

In the step 42, it is judged whether or not the engine key 5 is insertedinto the key cylinder 3. When it is judged that the engine key 5 isinserted, the procedure advances to step 43, and when it is judged thatthe engine key 5 is not inserted, the procedure returns to step 41.

Accordingly, when the control mode of “green key registration” starts,the display of “green key registration” of “each key registration mode”and ‘Please insert red key’ on the display part 29 continues until theengine key 5 is inserted into the key cylinder 3 to urge insertion ofthe red key 5C into the key cylinder 3.

In the step 43, it is judged whether or not the discrimination code ofthe engine key 5 inserted into the key cylinder 3 is identical with thediscrimination code of the red key 5C. When it is identical with thediscrimination code of the red key 5C, the procedure advances to step45, and when it is not identical with the discrimination code of the redkey 5C, the procedure advances to step 44 with displaying ‘Key does notcoincide’ on the display part 29 for a predetermined period of time(several seconds), and the procedure returns to step 41.

In step 45, it is judged whether or not the cryptographic code of theengine key 5 inserted into the key cylinder 3 is identical with thecryptographic code recorded in the immobilizer control unit 17. When thecryptographic codes are identical, the procedure advances to step 46,and when the cryptographic codes are not identical, ‘Key does notcoincide’ is displayed on the display part 29 in step 44, and theprocedure returns to step 41.

Accordingly, when the engine key 5 other than the registered red key 5Cis inserted into the key cylinder 3, after it is notified that theerroneous key different from the red key 5C has been inserted into thekey cylinder 3 by displaying ‘Key does not coincide’ on the display part29, the insertion of the red key 5C into the key cylinder 3 is urgedagain.

In the step 45, when the cryptographic codes are judged to be identical,the procedure advances to step 46, and in the step 46, ‘Please insertgreen key’ is displayed on the display part 29 (until a new key isinserted into the key cylinder 3) and the procedure advances to step 47.

In the step 47, it is judged whether or not the engine key 5 insertedinto the key cylinder 3 can be registered. In this step, when theinserted engine key 5 is the master key or the slave key of the greenkey, that is, when the cryptographic code is recorded in the insertedengine key 5, and the discrimination code of the master key of the greenkey or the slave key of the green key is recorded in the memory area ofthe discrimination code of the engine key 5, the key is judged to beregistrable, and the procedure advances to step 49. In the case wherethe discrimination code of the engine key 5 inserted into the keycylinder 3 is the discrimination code other than the discrimination codeof the master key or the slave key of the green key, in the case wherethe discrimination code is not recorded, or in the case where thecryptographic code is not recorded, the key is judged to beunregistrable, and the procedure advances to step 48. In the step 48,‘This key can not be registered’ is displayed on the display part 29,and the procedure returns to step 46.

Accordingly, in the case where the cryptographic code is recorded in theinserted engine key 5 and the discrimination code of the master key orthe slave key of the green key is recorded in the memory area of thediscrimination code of the engine key 5, the key can be registered asthe green key 5D (master key or slave key), and the engine key 5 otherthan this can not be registered.

In the step 49, the cryptographic code of the engine key 5 inserted intothe key cylinder 3 is written into the memory area, corresponding to themaster key of the green key, in the EEPROM 24 of the immobilizer controlunit 17, and at this time, the same cryptographic code is simultaneouslywritten into the memory area, corresponding to the slave key of thegreen key, in the EEPROM 24, and the registration operation of the greenkey ends.

Accordingly, among the engine keys 5, with respect to the key in whichthe cryptographic code is recorded and the discrimination code of themaster key or the slave key of the green key is recorded, the ID code ofthe engine key 5 corresponds to the ID code of the immobilizer controlunit 17 so that the green key is registered to serve as the allowancekey, and this master key of the green key 5D or slave key of the greenkey 5D can allow the rewriting or writing of the ID code.

Accordingly, for example, as shown in the left table of FIG. 17, inorder to register the green key 5D, in the case where the memory areasof the cryptographic codes of the master key and the slave key of thegreen key of the EEPROM 24 of the immobilizer control unit 17 are blank,and the green key is not registered, the master key or the slave key ofthe green key in which the cryptographic code of [k] is recorded, asshown in the right table of FIG. 17, enables the cryptographic code of[k] to be recorded into the memory area corresponding to the master keyof the green key and the memory area corresponding to the slave key ofthe green key of the EEPROM 24 of the immobilizer control unit 17, asshown in the left table of FIG. 18, whereby the green key 5D isregistered, and the master key of the green key 5D or the slave key ofthe green key 5D can allow the rewriting or writing of the ID codesimilarly to the red key 5C.

Further, in the registration operation of the green key, differentlyfrom the registration operation of the blue key, since the registrationof the cryptographic code is not rendered impossible, the registeredgreen key 5D can also be registered as the green key 5D into theimmobilizer control unit 17 of another work machine.

Incidentally, in the operation procedure of the control mode of “greenkey registration”, when one of the master key of the green key 5D andthe slave key of the green key 5D is registered, the cryptographic codeof the green key 5D is written into the memory area, corresponding tothe master key of the green key 5D, in the EEPROM 24 of the immobilizercontrol unit 17, and simultaneously, the identical cryptographic code iswritten into the memory area corresponding to the slave key of the greenkey 5D, so that both the master key of the green key 5D and the slavekey of the green key 5D are registered. Alternatively, the memory areaof the cryptographic code, corresponding to the master key of the yellowkey 5B, in the EEPROM 24 may be made in common with the memory area ofthe cryptographic code corresponding to the slave key of the green key5D, so that the registration operation of one of the master key of thegreen key 5D and the slave key of the green key 5D can register both ofthe master key of the green key 5D and the slave key of the green key5D. Alternatively, the master key of the green key 5D and the slave keyof the green key 5D may be separately registered.

Next, the operation procedure of the control mode of “yellow key copy”in “each key copy mode” will be described with reference to flowchartsof FIG. 19( a) and FIG. 19( b).

When the control mode of “yellow key copy” of “each key copy mode”starts, in step 61, the display part 29 displays “yellow key copy” of“each key copy” and ‘Please insert yellow key’, and the procedureadvances to step 62.

In the step 62, it is judged whether or not the engine key 5 is insertedinto the key cylinder 3. When it is judged that the engine key 5 isinserted, the procedure advances to step 63, and when it is judged thatthe engine key 5 is not inserted, the procedure returns to step 61.

Accordingly, when the control mode of “yellow key copy” starts, untilthe engine key 5 is inserted into the key cylinder 3, the display part29 continues to display “yellow key copy” of “each key copy mode” and‘Please insert yellow key’ to urge the insertion of the master key ofthe yellow key 5B into the key cylinder 3.

In the step 63, it is judged whether or not the master key of the yellowkey 5B is inserted into the key cylinder 3, that is, whether or not theID code (cryptographic code and discrimination code) of the engine key 5inserted into the key cylinder 3 is identical with that of the masterkey of the yellow key 5B, and when it is judged that the master key ofthe yellow key 5B is inserted, the procedure advances to step 65. Whenit is judged that the master key of the yellow key 5B is not inserted,the procedure advances to step 64 with displaying ‘Key does notcoincide’ on the display part 29 for a predetermined period of time(several seconds), and the procedure returns to step 61.

Accordingly, when the engine key 5 other than the master key of theyellow key 5B is inserted into the key cylinder 3, after it is notifiedthat the erroneous key different from the master key of the yellow key5B has been inserted into the key cylinder 3 by displaying ‘Key does notcoincide’ on the display part 29, the insertion of the master key of theyellow key 5B into the key cylinder 3 is urged again.

When the procedure advances from step 63 to step 65, in the step 65, thecryptographic code of the master key of the yellow key 5B is writteninto the RAM 26 of the immobilizer control unit 17. In step 66, ‘Pleaseinsert key for copy’ is displayed on the display part 29 (until a newkey is inserted into the key cylinder 3), and the procedure advances tostep 67.

In the step 67, it is judged whether or not the inserted key is writablein this judgment, in the case where the discrimination code of the redkey 5C, the discrimination code of the master key of the yellow key 5B,or the discrimination code of the master key of the green key 5D is notrecorded in the memory area of the discrimination code of the insertedengine key 5, that is, where the memory areas of the cryptographic codeand the discrimination code are blank (blank key), or the cryptographiccode is recorded and the memory area of the discrimination code isblank, the key is judged to be registrable, and the procedure advancesto step 69. In the case where the discrimination code of the red key 5C,the discrimination code of the master key of the yellow key 5B, or thediscrimination code of the master key of the green key 5D is recorded asthe discrimination code of the engine key 5 inserted into the keycylinder 3, the key is judged to be unregistrable, and the procedureadvances to step 68. In the step 68, ‘This key can not be used for copy’is displayed on the display part 29 for a predetermined period of time(several seconds), and the procedure returns to step 66. However, as towhether or not the inserted key is writable, with respect to the bluekey 5A, the blue key 5A having been registered in the immobilizercontrol unit 17 is judged to be unwritable, while the unregistered bluekey 5A is judged to be writable.

Accordingly, when the unrewritable or unwritable engine key 5 isinserted into the key cylinder 3, after it is notified that theunrewritable red key 5C, master key of the yellow key 5B, master key ofthe green key 5D or registered blue key 5A, has been erroneouslyinserted into the key cylinder 3 by displaying ‘This key can not be usedfor copy’ on the display part 29, the insertion of a key for copy intothe key cylinder 3 is urged again.

In the step 67, when the inserted key is judged to be writable, theprocedure advances to step 69, and in the step 69, the discriminationcode of the slave key of the yellow key, and the cryptographic codeidentical with the cryptographic code of the master key of the yellowkey 5B are written into the EEPROM 11 of the engine key 5 for copy, ordata recorded in the EEPROM 11 of the engine key 5 for copy is rewrittento the discrimination code of the slave key of the yellow key and thecryptographic code identical with the cryptographic code of the masterkey of the yellow key 5B, whereby the ID code of the engine key 5 isrendered corresponding to the ID code of the immobilizer control unit 17so that the engine key 5 serves as the slave key of the yellow key 5B.As a result, the master key of the yellow key 5B is copied into theengine key 5, and the slave key of the yellow key 5B is formed.

In step 70, it is judged whether or not a further copy of the yellow keyis to be formed, and when it is judged that another copy of the yellowkey is to be formed, the procedure returns to step 66, and the nextcopying procedure of the yellow key is performed. The judgment as towhether or not the copy of the next yellow key is to be formed is madeaccording to, for example, whether or not the first switch 31 isoperated to be ON within a predetermined period of time. When the firstswitch 31 is operated to be ON, it is judged that the copying procedureof the yellow key 5B is to be performed, and the procedure returns tostep 66, and when the first switch 31 is not operated to be ON withinthe predetermined period of time, it is judged that the copyingprocedure of the yellow key is not to be performed, and the copyoperation of the yellow key 5B ends. Accordingly, the copying procedureof the yellow key can be performed continuously with respect to pluralengine keys 5.

Accordingly, in the case where data of the master key (origin of copy)of the yellow key 5B in which the cryptographic code of [f] and thediscrimination code of [t] are recorded as shown in the upper left tableof FIG. 20 is copied into the blank key (destination of copy) in whichthe cryptographic code and the discrimination code are not recorded asshown in the upper right table of FIG. 20, the cryptographic code of [f]and the discrimination code of [u] are recorded in the memory area ofthe EEPROM 11 of the engine key 5, as shown in the lower right table ofFIG. 20. As a result, the slave key of the yellow key 5B is formed fromthe blank key, and the engine can be started by this key.

Further, for example, in the case where data of the master key (originof copy) of the yellow key 5B in which the cryptographic code of [f] andthe discrimination code of [t] are recorded as shown in the upper lefttable of FIG. 21 is copied into the engine key 5 (destination of copy)in which the cryptographic code of [1] is recorded and thediscrimination code is not recorded as shown in the upper right table ofFIG. 21, the cryptographic code is rewritten to [f] and recorded intothe memory area of the cryptographic code of the EEPROM 11 of the enginekey 5, and the discrimination code of [u] is written into the memoryarea of the discrimination code of the EEPROM 11 of the engine key 5 andis recorded, as shown in the lower right table of FIG. 21. As a result,the slave key of the yellow key 5B is formed from the engine key 5 inwhich the cryptographic code is recorded, and the engine can be startedby this key.

Next, the operation procedure of the control mode of “green key copy” in“each key copy mode” will be described with reference to flowcharts ofFIG. 22( a) and FIG. 22( b).

When the control mode of “green key copy” of “each key copy mode”starts, in step 81, the display part 29 displays “green key copy” of“each key copy mode” and ‘Please insert green key’, and the procedureadvances to step 82.

In the step 82, it is judged whether or not the engine key 5 is insertedinto the key cylinder 3. When it is judged that the engine key 5 isinserted, the procedure advances to step 83, and when it is judged thatthe engine key 5 is not inserted, the procedure returns to step 81.

Accordingly, when the control mode of “green key copy” starts, until theengine key 5 is inserted into the key cylinder 3, the display part 29continues to display “green key copy” of “each key copy mode” and‘Please insert green key’ to urge the insertion of the master key of thegreen key 5D into the key cylinder 3.

In the step 83, it is judged whether the master key of the green key 5Dis inserted into the key cylinder 3, that is, whether or not the ID code(cryptographic code and discrimination code) of the engine key 5inserted into the key cylinder 3 is identical with the master key of thegreen key 5D, and when it is judged that the master key of the green key5D is inserted, the procedure advances to step 85. When it is judgedthat the master key of the green key 5D is not inserted, the procedureadvances to step 84 with displaying ‘Key does not coincide’ on thedisplay part 29 for a predetermined period of time (several seconds),and the procedure returns to step 81.

Accordingly, when the engine key 5 other than the master key of thegreen key 5D is inserted into the key cylinder 3, after it is notifiedthat the erroneous key different from the master key of the green key 5Dhas been inserted into the key cylinder 3 by displaying ‘Key does notcoincide’ on the display part 29, the insertion of the master key of thegreen key 5D into the key cylinder 3 is urged again.

When the procedure advances from step 83 to step 85, in the step 85, thecryptographic code of the master key of the green key 5D is written intothe RAM 26 of the immobilizer control unit 17, and in step 86, ‘Pleaseinsert key for copy’ is displayed on the display part 29 (until a newkey is inserted into the key cylinder 3), and the procedure advances tostep 87.

In step 87, it is judged whether or not the inserted key is writable. Inthis judgment, in the case where the discrimination code of the red key5C, the discrimination code of the master key of the yellow key 5B, orthe discrimination code of the master key of the green key 5D is notrecorded in the memory area of the discrimination code of the insertedengine key 5, that is, where the memory areas of the cryptographic codeand the discrimination code are blank (blank key), or the cryptographiccode is recorded and the memory area of the discrimination code isblank, the key is judged to be writable, and the procedure advances tostep 89. In the case where the discrimination code of the red key 5C,the discrimination code of the master key of the yellow key 5B, or thediscrimination code of the master key of the green key 5D is recorded asthe discrimination code of the engine key 5 inserted into the keycylinder 3, the key is judged to be unwritable, and the procedureadvances to step 88. In the step 88, ‘This key can not be used for copy’is displayed on the display part 29 for a predetermined period of time(several seconds), and the procedure returns to step 86. However, as towhether or not the inserted key is writable, with respect to the bluekey 5A, the blue key 5A having been registered in the immobilizercontrol unit 17 is judged to be unwritable, while the unregistered bluekey 5A is judged to be writable.

Accordingly, when the unrewritable or unwritable engine key 5 isinserted into the key cylinder 3, after it is notified that theunrewritable red key 5C, master key of the yellow key 5B, master key ofthe green key 5D or registered blue key 5A has been erroneously insertedinto the key cylinder 3 by displaying ‘This key can not be used forcopy’ on the display part 29, the insertion of a key for copy into thekey cylinder 3 is urged again.

In the step 87, when the inserted key is judged to be writable, theprocedure advances to step 89. In the step 89, the discrimination codeof the slave key of the green key 5D, and the cryptographic codeidentical with the cryptographic code of the master key of the green key5D are written into the EEPROM 11 of the engine key 5 for copy, or datarecorded in the EEPROM 11 of the engine key 5 for copy is rewritten tothe discrimination code of the slave key of the green key 5D and thecryptographic code identical with the cryptographic code of the masterkey of the green key 5D, whereby the ID code of the engine key 5 isrendered corresponding to the ID code of the immobilizer control unit 17so that the engine key 5 functions as the slave key of the green key 5D,and as a result, the master key of the green key 5D is copied into theengine key 5, and the slave key of the green key 5D is formed.

In step 90, it is judged whether or not a further copy of the green keyis to be formed, and when it is judged that another copy of the greenkey is to be formed, the procedure returns to step 86, and the nextcopying procedure of the green key is performed. The judgment as towhether or not the copy of the green key is to be formed is madeaccording to, for example, whether or not the first switch 31 isoperated to be ON within a predetermined period of time. When the firstswitch 31 is operated to be ON, it is judged that the copying process ofthe green key is to be performed, and the procedure returns to step 66.When the first switch 31 is not operated to be ON within thepredetermined period of time, it is judged that the copying procedure ofthe green key is not to be performed, and the copy operation of thegreen key is ends. Accordingly, the copying procedure of the green keycan be performed continuously with respect to plural engine keys 5.

Accordingly, for example, in the case where the data of the master key(origin of copy) of the green key 5D in which the cryptographic code of[k] and the discrimination code of [w] are recorded as shown in theupper left table of FIG. 23 is copied into the blank key (destination ofcopy) in which the cryptographic code and the discrimination code arenot recorded as shown in the upper right table of FIG. 23, thecryptographic code of [k] and the discrimination code of [x] arerecorded into the EEPROM 11 of the engine key 5 as shown in the lowerright table of FIG. 23. As a result, the slave key of the green key 5Dis formed from the blank key, and the engine can be started by this key.

Further, for example, in the case where the data of the master key(origin of copy) of the green key 5D in which the cryptographic code of[k] and the discrimination code of [w] are recorded as shown in theupper left table of FIG. 24 is copied into the engine key 5 (destinationof copy) in which the cryptographic code of [1] is recorded and thediscrimination code is not recorded as shown in the upper right table ofFIG. 24, the cryptographic code of [k] is rewritten and recorded intothe memory area of the cryptographic code of the EEPROM 11 of the enginekey 5, and the discrimination code of [x] is written and is recordedinto the memory area of the discrimination code of the EEPROM 11 of theengine key 5 as shown in the lower right table of FIG. 24,. As a result,the slave key of the green key 5D is formed from the engine key 5 inwhich the cryptographic code is recorded, and the engine can be startedby this key.

Next, the procedure of the starting operation of the engine the blue key5A or the yellow key 5B (including both the master key and the slavekey) will be described with reference to flowcharts of FIG. 25( a) andFIG. 25( b).

In step 101, it is judged whether or not the engine key 5 inserted intothe key cylinder 3 is the blue key 5A or the yellow key 5B, that is,whether or not the discrimination code recorded in the engine key 5 isidentical with the discrimination code of the blue key 5A or the yellowkey 5B recorded in the ROM 25 of the immobilizer control unit 17. Whenit is judged that the blue key 5A or the yellow key 5B is inserted, theprocedure advances to step 103, and when it is judged that the blue key5A or the yellow key 5B is not inserted, the procedure advances to step102. In the step 102, ‘Key does not coincide’ is displayed on thedisplay part 29, and the procedure returns to step 101.

Accordingly, when the discrimination code of the engine key 5 insertedinto the key cylinder 3 is not identical with the discrimination code ofthe blue key 5A or the yellow key 5B recorded in the immobilizer controlunit 17, ‘Key does not coincide’ is displayed on the display part 29,and the starting of the engine is not allowed.

In the step 103, it is judged whether or not the cryptographic code ofthe engine key 5 inserted into the key cylinder 3 is identical with thecryptographic code of the immobilizer control unit 17, that is, whetheror not the cryptographic code recorded in the EEPROM 11 of the enginekey 5 is identical with the cryptographic code recorded in the memoryarea, corresponding to the discrimination code of the blue key 5A or theyellow key 5B, of the EEPROM 24 of the immobilizer control unit 17, andwhen they are identical, the procedure advances to step 104. When theyare not identical, the procedure advances to step 102 with displaying‘Key does not coincide’ on the display part 29, and the procedurereturns to step 101.

Accordingly, when the cryptographic code of the engine key 5 insertedinto the key cylinder 3 is not identical with the cryptographic coderecorded in the immobilizer control unit 17, ‘Key does not coincide’ isdisplayed on the display part 29, and the starting of the engine is notallowed.

In step 104, a random number is transmitted to the inserted engine key 5from the immobilizer control unit 17, and in step 105, the engine key 5receives the random number, calculates the exclusive OR of the randomnumber and the cryptographic code of the engine key 5, and transmits thecalculated value to the immobilizer CPU 23 of the immobilizer controlunit 17. For example, where the random number is 1234 (hexadecimalnumber) and the cryptographic code is 5678 (hexadecimal number), theexclusive OR thereof is 444C (hexadecimal number), and therefore, 444Cis transmitted to the immobilizer CPU 23.

In step 106, the immobilizer CPU 23 calculates the exclusive OR of thecalculated value (444C) from the engine key 5 and the transmitted randomnumber (1234), and in step 107, it is judged whether or not thecalculated value of the immobilizer CPU 23 of the immobilizer controlunit 17 is identical with the cryptographic code. When they areidentical, the procedure advances to step 108, and when they are notidentical, the procedure returns to step 102. In the above example,since the calculated value is 444C (hexadecimal number) and the randomnumber is 1234 (hexadecimal number), the calculated value of theexclusive OR thereof is 5678 (hexadecimal number).

In the step 108, the engine start signal S is outputted from theimmobilizer control unit 17 to the engine control unit 19, therebystarting the engine. Accordingly, the ID code of the engine key 5 (theblue key 5A or the yellow key 5B) inserted into the key cylinder 3 iscollated with the ID code recorded in the immobilizer control unit 17,and when the result of collation is affirmative, the starting of theengine by the engine key 5 (the blue key 5A or the yellow key 5B) isallowed. Since the calculation by the exclusive OR is interposed in thiscollation, it is possible to more certainly prevent an erroneousaffirmative result of the collation due to a wrong operation and anerroneous start of the engine by an invalid key.

The operation procedure of the control mode of “red key use” in “vehicleresale mode” will be described with reference to a flowchart of FIG. 28.

When the control mode of “red key use” of “vehicle resale mode” starts,in step 201, the display part 29 displays “red key use” of “vehicleresale mode” and ‘Please insert red key’, and the procedure advances tostep 202.

In the step 202, it is judged whether or not the engine key 5 isinserted into the key cylinder 3. When it is judged that the engine key5 is inserted, the procedure advances to step 203, and when it is judgedthat the engine key 5 is not inserted, the procedure returns to step201.

Accordingly, when the control mode of “red key use” of “vehicle resalemode” starts, until the engine key 5 is inserted into the key cylinder3, the display part 29 continues to display “red key use” of “vehicleresale mode” and ‘Please insert red key’ to urge the insertion of thered key 5C into the key cylinder 3.

In the step 203, it is judged whether or not the discrimination code ofthe engine key 5 inserted into the key cylinder 3 is identical with thediscrimination code of the red key 5C (judgment is made as to whether ornot it is the red key 5C). When it is identical with the discriminationcode of the red key 5C, the procedure advances to step 205, and when itis not identical with the discrimination code of the red key 5C, theprocedure advances to step 204 with displaying ‘Key does not coincide’on the display part 29 for a predetermined period of time (severalseconds), and the procedure returns to step 201.

In the step 205, it is judged whether or not the cryptographic code ofthe engine key 5 (the red key 5C) inserted into the key cylinder 3 isidentical with the cryptographic code corresponding to the red key 5Crecorded in the immobilizer control unit 17. When the cryptographiccodes are identical, the procedure advances to step 206, and when thecryptographic codes are not identical, the procedure returns to step 204with displaying ‘Key does not coincide’ on the display part 29 andfurther returns to step 201.

Accordingly, when the engine key 5 other than the red key 5C is insertedinto the key cylinder 3, after it is notified that the erroneous keydifferent from the red key 5C has been inserted into the key cylinder 3by displaying ‘Key does not coincide’ on the display part 29, theinsertion of the red key 5C into the key cylinder 3 is urged again.

In the step 206, the memory area of the cryptographic code correspondingto the yellow key 5B recorded in the EEPROM 24 of the immobilizercontrol unit 17 is cleared, and the memory area of the cryptographiccode corresponding to the green key 5D is cleared (deleted).

For example, in the case where the cryptographic code is recorded in theEEPROM 24 of the immobilizer control unit 17 as shown in FIG. 29, whenthis “vehicle resale mode” is executed, the ID code of the red key 5C iscollated with the ID code corresponding to the red key recorded in theimmobilizer control unit 17. When the result of the collation isaffirmative (steps 203, 205), the memory areas ([f], [k]) of thecryptographic code of the yellow key 5B and the cryptographic code ofthe green key 5D recorded in the EEPROM 24 of the immobilizer controlunit 17 are cleared, as shown in FIG. 30 (step 206). As a result, it ispossible to prevent the engine from being started by the yellow key 5Bwhich can start engines of plural work machines, and it is also possibleto prevent the blue key 5A and the yellow key 5B from being registeredby the green key 5D previously stored in the EEPROM 24 of theimmobilizer control unit 17.

The operation procedure of the control mode of “special manipulation” in“vehicle resale mode” will be described with reference to flowcharts ofFIG. 31( a) and FIG. 31( b).

When the control mode of “special manipulation” of “vehicle resale mode”starts, in step 210, the display part 29 displays “special manipulation”of “vehicle resale mode” and ‘Please insert key’, and the procedureadvances to step 211.

In the step 211, it is judged whether or not the engine key 5 isinserted into the key cylinder 3. When it is judged that the engine key5 is inserted, the procedure advances to step 212, and when it is judgedthat the engine key 5 is not inserted, the procedure returns to step210.

Accordingly, when the control mode of “special manipulation” of “vehicleresale mode” starts, until the engine key 5 is inserted into the keycylinder 3, the display part 29 continues to display “specialmanipulation” of “vehicle resale mode” and ‘Please insert key’ to urgethe insertion of the engine key 5 into the key cylinder 3 by the displaypart 29.

In the step 212, an internal timer incorporated in the immobilizer CPU23 of the immobilizer control unit 17 is actuated.

In step 213, the immobilizer CPU 23 of the immobilizer control unit 17counts, using the signal from the key cylinder 3, how many times theignition switch 2 has been rotated from the OFF position to the ONposition (number of times of ON-OFF rotation) by the engine key 5 afterthe internal timer of the immobilizer CPU 23 of the immobilizer controlunit 17 was actuated (after the engine key 5 was inserted into the keycylinder 3), and it is judged whether or not the number of times ofON-OFF rotation of the ignition switch 2 in a predetermined period oftime T1 after the internal timer of the immobilizer CPU 23 of theimmobilizer control unit 17 was actuated is N times. When the number oftimes of ON-OFF rotation of the ignition switch 2 in the predeterminedperiod of time T1 is N times, the internal timer of the immobilizer CPU23 of the immobilizer control unit 17 is cleared, and the procedureadvances to step 215, and otherwise, the number of times of rotation ofthe ignition switch 2 is judged to be an invalid number of times, andthe procedure advances to step 214.

For example, assuming the predetermined period of time T1 to be 10seconds and the number of times of ON-OFF rotation N to be ten times, instep 213, every turning motion of the ignition switch 2 from the OFFposition to the ON position is counted as one, and when the number oftimes of ON-OFF rotation after the predetermined period of time of 10seconds is ten times, the procedure advances to step 215. When thenumber of times of ON-OFF rotation after the predetermined period oftime of 10 seconds is other than ten times (for example, seven or twelvetimes), the procedure advances to step 214.

In the step 215, ‘Please proceed with the next step’ is displayed on thedisplay part.

In step 216, it is judged whether or not the engine key 5 is insertedinto the key cylinder 3. When it is judged that the engine key 5 isinserted, the procedure advances to step 217, and when it is judged thatthe engine key 5 is not inserted, the procedure returns to step 215.

In the step 217, the internal timer incorporated in the immobilizer CPU23 of the immobilizer control unit 17 is actuated.

In step 218, similarly to the above, the immobilizer CPU 23 of theimmobilizer control unit 17 counts how many times the ignition switch 2has been rotated by the engine key 5 from the OFF position to the ONposition after the internal timer of the immobilizer CPU 23 of theimmobilizer control unit 17 was actuated (after the engine key 5 wasinserted into the key cylinder 3), and it is judged whether or not thenumber of times of ON-OFF rotation of the ignition switch 2 in apredetermined period of time T2 is L times. When the number of times ofON-OFF rotation of the ignition switch 2 in the predetermined period oftime T2 is L times, the internal timer of the immobilizer CPU 23 of theimmobilizer control unit 17 is cleared, and the procedure advances tostep 219, and otherwise, the number of times is judged to be an invalidnumber of times, and the procedure advances to step 214. In the step214, ‘ID can not be deleted’ is displayed on the display part 29 for apredetermined period of time, and the procedure returns to step 210.

In step 219, the memory area of the cryptographic code corresponding tothe yellow key 5B recorded in the EEPROM 24 of the immobilizer controlunit 17 is cleared, and the memory area of the cryptographic codecorresponding to the green key 5D is cleared.

Accordingly, in the control mode of “special manipulation” of “vehicleresale mode”, the cryptographic codes of the yellow key 5B and the greenkey 50 recorded in the immobilizer control unit 17 can be deleted byperforming the special manipulation which is different from operationsfor starting engine (the ignition switch 2 is rotated from the OFFposition to the ON position successively within a predetermined periodof time) with the engine key 5 (key capable of rotating the ignitionswitch 2 from the OFF position to the ON position).

Since such a special manipulation is different from operations forstarting engine, it is difficult that a person who intends to steal themachine carries out a similar operation, and hence, the antitheftfunction is not ruined.

Further, by providing two patterns of special manipulations such as thestep 213 and step 218, the rotation operation of the engine key 5 iscomplicated, and the antitheft function is improved. Incidentally, byincreasing the special manipulation as in the step 213 and step 218, theantitheft function can be improved.

The operation procedure of the control mode of “keyless” in “emergencystart mode” will be described with reference to a flowchart of FIG. 32.

When the control mode of “keyless” of “emergency start mode” starts, instep 220, the display part 29 displays “keyless” of “emergency startmode”, and the immobilizer CPU 23 of the immobilizer control unit 17reads an engine starting code recorded in the ROM 25 and a calculationcode.

In step 221, the immobilizer CPU 23 of the immobilizer control unit 17calculates the exclusive OR (XOR) of the engine starting code and thecalculation code, and converts the engine starting code into a vehicleregistration number.

In step 222, the vehicle registration number is displayed on the displaypart 29 (display means), and ‘Please input personal identification code’is displayed on the display part 29, so that a code can be inputted bythe input means, and the procedure advances to step 223.

In the step 223, it is judged whether or not the input of the code hasbeen completed by the input means (the first switch 31, the secondswitch 32, and the third switch 33), that is, it is judged whether ornot the third switch is pressed in the input state. When the input ofthe code is completed, the procedure advances to step 224, andotherwise, the procedure returns to step 222.

In the step 224, when the input code inputted by the input means isidentical with the engine starting code, the procedure advances to step226, and otherwise, the procedure advances to step 225.

In the step 225, ‘Personal identification code is not identical’ isdisplayed on the display part 29 for a predetermined period of time, andthe procedure returns to step 222.

In the step 226, the immobilizer CPU 23 of the immobilizer control unit17 outputs the engine start signal S to the engine control unit 19(ECU).

Accordingly, when the engine starting code is identical with the inputcode, the engine starting is allowed, and when the engine starting codeis not identical with the input code, the engine starting is notallowed. By knowing the engine starting code recorded in the immobilizercontrol unit 17, the engine can be started.

However, in the control mode of “keyless” of “emergency start mode”,since the engine starting code is converted into the vehicleregistration number by using the conversion function (step 220, step221), the engine starting code can not be directly known, and insteadthereof, the vehicle registration number (dummy engine starting code)can be known by the display means 29 (step 222).

When a method of calculating the engine starting code from the vehicleregistration number, that is, the conversion function provided in theimmobilizer control unit 17 is known, the engine starting code can becalculated from the vehicle registration number.

That is, as is understood from step 221, since the vehicle registrationnumber is a calculated value of the exclusive OR of the engine startingcode and the calculation code, when the exclusive OR of the vehicleregistration number and the calculation code is calculated, the value ofthe engine starting code is restored.

For example, assuming the engine starting code recorded in the ROM 25 ofthe immobilizer control unit 17 to be 5678 (hexadecimal number) and thecalculation code recorded in the ROM 25 of the immobilizer control unit17 to be 1234 (hexadecimal number), the exclusive OR of the enginestarting code and the calculation code, that is, the vehicleregistration number is 444C (hexadecimal number). When the exclusive ORof the vehicle registration number 444C and the calculation code 1234(hexadecimal number) is calculated, the value is 5678 (hexadecimalnumber), and this value is equal to the engine starting code 5678(hexadecimal number).

However, since the engine starting code, the calculation code, therelation between the engine starting code and the vehicle registrationnumber, and the like are previously recorded as a control program in theimmobilizer control unit 17, in general, even if only the vehicleregistration number is known, the relation to the engine starting codeis not known, and the engine starting code can not be figured out fromthe vehicle registration number.

Accordingly, as described later, unless the user owning a work machinemakes inquiries to the manufacturer of the work machine (antitheftdevice 1) which manages the vehicle registration number, to learn theengine starting code (personal identification code) from themanufacturer, or unless the user owning the work machine learns themethod of figuring out the engine starting code from the vehicleregistration number from the work machine manufacturer or the like, theengine starting code can not be found.

Next, the method of figuring out the engine starting code (personalidentification code) from the vehicle registration number will bedescribed.

For example, work machines owned by a rental company or the like are, asshown in FIG. 26, stored in respective branches, and the vehicleregistration number of each of the work machines in the respectivebranches is generally managed by a dealer (or manufacturer) whichmanufactures or sells the work machine (antitheft device 1).

As shown in FIG. 34, in the manufacturer, the vehicle registrationnumbers and the engine starting codes are recorded in a recording mediumsuch as a personal computer 40 installed in the manufacturer, so thatthe engine starting code can be figured out from the vehicleregistration number, and the vehicle registration numbers and the enginestarting codes are managed not to be leaked from the manufacturer tooutside.

When the vehicle registration number is known by the control mode of“keyless” of “emergency start mode”, for example, a user using the workmachines of the respective branches of the rental company uses atelephone 41 or the like (communication means) installed in each branchof the rental company to make a telephone call to a service center 43 ofthe manufacturer managing the vehicle registration numbers. Themanufacturer receives the telephone communication from the user by atelephone 44 installed in the manufacturer, inputs the vehicleregistration number transmitted from the user through the telephone lineto the personal computer 40 or the like storing the vehicle registrationnumbers and the engine starting codes, and causes a display device 45(monitor) of the personal computer 40 or the like to display userinformation of the work machine of the vehicle registration number.

At this time, the manufacturer managing the vehicle registration numberscollates information identifiying the user, such as the user's name,telephone number, and birth date, obtained from the user with the userinformation of the work machine of the vehicle registration numberdisplayed on the monitor 45 of the personal computer 40 or the like.When the information obtained from the user having made a telephone callcoincides with the user information displayed on the monitor 45, it isjudged that the user having made the telephone call is valid.

Incidentally, when the manufacturer sells the work machine (antitheftdevice 1) to the rental company or the personal user (user), if the userinformation (information for identification, such as the user'stelephone number, birth date and address, personal identification numberstated to the manufacturer at the time of purchasing the work machine),which links the vehicle registration number of the sold work machine tothe user, is previously registered in the personal computer 40 of themanufacturer, and the user information of the work machine is arrangedto be displayed on the monitor 45 or the like by imputting the vehicleregistration number, it is possible, as stated above, to judge whetheror not the person having made the telephone call is a valid user bycollating the user information of the vehicle registration number withthe information obtained through the telephone.

When it is judged that the user is valid, the engine starting code iscalculated from the vehicle registration number by the personal computer40 of the manufacturer, and the manufacturer transmits the calculatedengine starting code as the personal identification code to the userthrough the telephone 45 and the telephone line.

The procedure of above operation of the personal computer 40 of themanufacturer managing the vehicle registration numbers flows as followsas shown in FIG. 35.

In step 280, it is judged whether or not the input of the vehicleregistration number is completed. When the input is completed, theprocedure advances to step 281.

In the step 281., the user information, such as name, telephone number,birth date of user owning the work machine of the vehicle registrationnumber, and personal identification number stated to the manufacturer orthe like at the time of purchasing the work machine, is displayed.

In step 282, the calculation code recorded in the recording medium ofthe personal computer 40 is read. This calculation code is identicalwith the calculation code recorded in the immobilizer control unit 17 ofthe work machine of the vehicle registration number.

In step 283, the exclusive OR (XOR) of the vehicle registration numberand the calculation code recorded in the recording medium of thepersonal computer 40 is calculated.

In step 284, the calculated value figured out in step 283 is displayedas the personal identification code.

Accordingly, since the calculation code and the calculation methodrecorded in the personal computer 40 or the like of the manufacturermanaging the vehicle registration numbers are identical with thecalculation code and the calculation method recorded in the work machine(antitheft device 1) displaying the vehicle registration number, theengine starting code can be figured out from the vehicle registrationnumber.

For example, assuming the engine starting code recorded in theimmobilizer control unit 17 to be 5678 (hexadecimal number) and thecalculation code recorded in the immobilizer control unit 17 and thepersonal computer 40 of the manufacturer to be 1234 (hexadecimalnumber), the vehicle registration number displayed on the work machineis 444C (hexadecimal number). When this vehicle registration number isinputted to the personal computer 40 of the manufacturer, the personalidentification code displayed on the monitor of the manufacturer is 5678(hexadecimal number), whereby the engine starting code 5678 can befigured out from the vehicle registration number 444C.

Accordingly, unless the procedure as stated above is performed, theengine starting code can not be known. Further, it is generally known toonly the user owning the work machine, the manufacturer and the likethat the personal identification code can be figured our by transmittingthe vehicle registration number to the manufacturer. Accordingly, forexample, even if a person who intends to steal the machine can know thevehicle registration number, it is difficult to know that the personalidentification code must be figured out by performing the procedure asstated above.

Even if the person trying to steal the machine can know that thepersonal identification code can be figured out by transmitting thevehicle registration number to the manufacturer, since the manufacturerjudges whether or not the person is a valid user by the userinformation, it is difficult that the person trying to steal the machineobtains the personal identification code from the vehicle registrationnumber by making a telephone call to the manufacturer.

Incidentally, in the above embodiment, the engine starting code isfigured out from the conversion code (vehicle registration number) bythe transmission of the vehicle registration number from the user to themanufacturer and the calculation of the vehicle registration number bythe personal computer 40 of the manufacturer. Alternatively, themanufacturer may prepare a table of the engine starting code and thevehicle registration number, which shows the correspondence between thevehicle registration number and the engine starting code for figuringout the engine start code from the vehicle registration number, andprovide the rental company or personal user with the table, so that therental company or personal user can figure out the engine starting codefrom the table only when the engine is started by the engine startingcode, and manage to make it secret that the table indicates the enginestarting code when the table is not used. Alternatively, themanufacturer may prepare a device which can display the engine startingcode when the vehicle registration number is inputted, and provide therental company or personal user with the device, so that the rentalcompany or personal user can figure out the engine starting code by thedevice only when the engine is started by the engine starting code, andmanage to make it secret that this device displays the engine startingcode when the device is not used.

With this procedure, the engine starting code can be figured out fromthe vehicle registration number without the inquiries to themanufacturer. It is preferable that the table of the vehicleregistration numbers and the engine starting codes or the device, whichcan display the engine starting code when the vehicle registrationnumber is inputted, is kept in the safe of the rental company orpersonal user, so that the engine starting code is strictly protectedfrom being known easily.

Incidentally, although the engine starting code is converted intoanother code and the code is displayed as the vehicle registrationnumber, this converted code may be any code as long as it can specifythe work machine. That is, the engine starting code may be convertedinto another code which may be displayed as the user registration numberor any other code numbers.

The operation procedure of the control mode of “special manipulation” of“emergency start mode” will be described with reference to FIG. 33( a)and FIG. 33( b).

The operation procedure of the control mode of “special manipulation” of“emergency start mode” will be described with reference to flowcharts ofFIG. 33( a) and FIG. 33( b).

When the control mode of “special manipulation” of “emergency startmode” starts, in step 230, the display part 29 displays “specialmanipulation” of “emergency start mode” and ‘Please insert key’, and theprocedure advances to step 231.

In the step 231, it is judged whether or not the engine key 5 isinserted into the key cylinder 3. When it is judged that the engine key5 is inserted, the procedure advances to step 232, and when it is judgedthat the engine key 5 is not inserted, the procedure returns to step230.

Accordingly, when the control mode of “special manipulation” of“emergency start mode” starts, until the engine key 5 is inserted intothe key cylinder 3, the display part 29 continues to display “specialmanipulation” of “emergency start mode” and ‘Please insert key’ to urgethe insertion of the engine key 5 into the key cylinder 3.

In the step 232, the internal timer incorporated in the immobilizer CPU23 of the immobilizer control unit 17 is actuated.

In step 233, the immobilizer CPU 23 of the immobilizer control unit 17counts, using the signal from the key cylinder 3, how many times theignition switch 2 has been rotated from the OFF position to the ONposition (the number of times of ON-OFF rotation) by the engine key 5after the internal timer of the immobilizer CPU 23 of the immobilizercontrol unit 17 was actuated (after the engine key 5 was inserted intothe key cylinder 3), and it is judged whether or not the number of timesof ON-OFF rotation of the ignition switch in a predetermined period oftime T1 after the internal timer of the immobilizer CPU 23 of theimmobilizer control unit 17 was actuated is N times. When the number oftimes of ON-OFF rotation of the ignition switch 2 in the predeterminedperiod of time T1 is N times, the internal timer of the immobilizer CPU23 of the immobilizer control unit 17 is cleared, and the procedureadvances to next step 235, and otherwise, the number of times ofrotation of the ignition switch 2 is judges to be an invalid number oftimes, and the procedure advances to step 234.

For example, assuming the predetermined time T1 to be made 10 secondsand the number of times of ON-OFF rotation to be ten times, in the step233, every turning motion of the ignition switch 2 from the OFF positionto the ON position is counted as one, and when the number of times ofON-OFF rotation in the predetermined period of time of ten seconds isten times, the procedure advances to step 235, and when the number oftimes of ON-OFF rotation in the predetermined period of time of tenseconds is other than ten times (for example, seven or twelve times),the procedure advances to step 234.

In the step 235, ‘Please proceed with next step’ is displayed on thedisplay part, and the procedure advances to step 236.

In the step 236, it is judged whether or not the engine key 5 isinserted into the key cylinder 3. When it is judged that the engine key5 is inserted, the procedure advances to step 237. When it is judgedthat the engine key 5 is not inserted, the procedure returns to step235.

In the step 237, the internal timer incorporated in the immobilizer CPU23 of the immobilizer control unit 17 is actuated.

In step 238, similarly to the above, the immobilizer CPU 23 of theimmobilizer control unit 17 counts how many times the ignition switch 2has been rotated by the engine key 5 from the OFF position to the ONposition after the internal timer of the immobilizer CPU 23 of theimmobilizer control unit 17 was actuated (after the engine key 5 wasinserted into the key cylinder 3), and it is judged whether or not thenumber of times of ON-OFF rotation of the ignition switch 2 in apredetermined period of time T2 is L times. When the number of times ofON-OFF rotation of the ignition switch 2 in the predetermined period oftime T2 is L times, the internal timer of the immobilizer CPU 23 of theimmobilizer control unit 17 is cleared, and the procedure advances tostep 239, and otherwise, the number of times is judged to be an invalidnumber of times, and the procedure advances to step 234. In the step234, ‘Engine can not be started’ is displayed on the display part 29 fora predetermined period of time, and the procedure returns to step 230.

In the step 239, the immobilizer CPU 23 of the immobilizer control unit17 outputs the engine start signal S to the engine control unit 19.

Accordingly, in the control mode of “special manipulation” of “emergencystart mode”, the engine can be started by performing the specialmanipulation which is different from operations for starting engine (theignition switch 2 is successively rotated from the OFF position to theON position within the predetermined period of time) with the engine key5 (key capable of rotating the ignition switch 2 from the OFF positionto the ON position).

The number of times N, L of ON-OFF rotation of the engine key 5 withinthe predetermined period of time is recorded in the immobilizer CPU 23of the immobilizer control unit 17, and the predetermined period of timeT1, T2 is also recorded in the immobilizer CPU 23 of the immobilizercontrol unit 17. Thus, in general, the number of times N, L of ON-OFFrotation, and the predetermined period of time T1, T2 are not known toeven the user owning the work machine, and unless the user owning thework machine makes inquiries to the manufacturer to learn the number oftimes N, L of ON-OFF rotation and the predetermined period of time T1,T2, or unless the user previously leans the special manipulation methodor the like from the manufacturer at the time of purchasing the workmachine or the like, the engine starting can not be performed.

For example, in the case where the user does not know the number oftimes N, L of ON-OFF rotation and the predetermined period of time T1,T2, similarly to the case where inquiries are made about the enginestarting key, the user of the work machine makes a telephone call to themanufacturer, notifies the user information (name, telephone number,birth date of the user owning the work machine, personal identificationnumber stated to the manufacturer at the time of purchasing the workmachine, and the like) to the manufacturer to prove that the user is acorrect user, and learns the special manipulation method for the workmachine from the manufacturer, so that the user is informed of thenumber of times N, L of ON-OFF rotation and the predetermined period oftime T1, T2, thereby allowing only the valid user to start the engine.

Further, since the user of the work machine can learn the number oftimes N, L of ON-OFF rotation and the predetermined period of time T1,T2 from the manufacturer at the time of purchasing the work machine orthe like, this special manipulation method can be known by only theuser.

Incidentally, although the number of times N, L of ON-OFF rotation andthe predetermined period of time T1, T2 are known by making inquiries tothe manufacturer, the manufacturer may prepare a diagram or the likeshowing the special manipulation method for the work machine, andprovide the rental company or personal user with the diagram, so thatthe rental company or personal user can perform the special manipulationto start the engine referring to the diagram showing the specialmanipulation only when the engine should be started by the specialmanipulation.

As described above, since the special manipulation is different fromoperations for starting engine and is complicated, it is difficult for aperson who intends to steal the machine to carry out the samemanipulation, and even in the case where the engine start key 5A, 5B islost, only the user can start the engine without ruining the antitheftfunction.

Further, by providing the two patterns of special manipulations such asthe step 233 and step 238, the antitheft function is improved.Incidentally, by increasing the special manipulation as in the step 233and step 238, the special manipulation becomes complicated, so that theantitheft function can be improved.

Further, even in the case where the antenna 15 provided in the keycylinder 3 fails and the ID code collation can not be performed betweenthe engine key 5 and the immobilizer control unit 17, the engine can bestarted by this special manipulation.

The operation procedure of the control mode of “keyless” in“initialization mode” will be described with reference to flowcharts ofFIG. 36( a) and FIG. 36( b).

When the control mode of “keyless” of “initialization mode” starts, instep 240, the display part 29 displays “keyless” of “initializationmode”, and the immobilizer CPU 23 of the immobilizer control unit 17reads the initialization code recorded in the ROM 25 and the calculationcode.

In step 241, the exclusive OR (XOR) of the initialization code and thecalculation code is calculated, and the initialization code is convertedinto a vehicle registration number.

In step 242, the vehicle registration number is displayed on the displaypart 29 (display means), and further, ‘Please input personalidentification code’ is displayed on the display part 29, so that a codecan be inputted by the input means, and the procedure advances to step243.

In the step 243, it is judged whether or not the input of the code iscompleted by the input means (the first switch 31, the second switch 32and the third switch 33), that is, it is judged whether or not the thirdswitch is pressed in the input state. When the input of the code iscompleted, the procedure advances to step 244, and otherwise, theprocedure returns to step 242.

In the step 244, when the input code inputted by the input means isidentical with the initialization code, the procedure advances to step246, and otherwise, the procedure advances to step 245.

In the step 245, ‘Personal identification code is not identical’ isdisplayed on the display part 29 for a predetermined period of time, andthe procedure returns to step 242.

In the step 246, ‘Please input personal identification code’ isdisplayed on the display part 29 for a predetermined period of time, andthe procedure advances to step 247.

In the step 247, when the engine key 5 having the cryptographic code isinserted into the key cylinder 3, the discrimination code of theimmobilizer control unit 17 corresponding to the red key 5C is writteninto the EEPROM 11 of the engine key 5 (for example, the blue key 5A),and the procedure advances to step 248.

In the step 248, the cryptographic code of the engine key 5 is writteninto the cryptographic code of the memory area of the red key 5C of theimmobilizer control unit 17.

Accordingly, among the engine keys 5, with respect to the engine key 5in which only the cryptographic code is recorded and the discriminationcode is not recorded, or the engine key 5 in which the cryptographiccode is recorded and the discrimination code of the red key 5C isrecorded, the ID code of the engine key 5 corresponds to the ID code ofthe immobilizer control unit 17, whereby the registration of the red keyis performed so that the key serves as the allowance key to form the newred key 5C, thereby allowing the rewriting or writing of the ID code bythis red key 5C.

In step 249, the cryptographic codes of the cryptographic codes (bluekey, yellow key, green key) other than the red key memory area of theimmobilizer control unit are cleared.

Accordingly, in the control mode of “keyless” of “initialization mode”,the engine key 5 having the ID code (cryptographic code) can beregistered as the red key 5C, and the cryptographic codes of the bluekey, the yellow key, and the green key recorded in the immobilizercontrol unit 17 are cleared. Thus, it is possible to obtain theinitialized state similar to FIG. 5 in which the cryptographic code ofonly the red key 5C is written in the EEPROM 24 of the immobilizercontrol unit 17, and when the yellow key 5B or the blue key is newlyregistered in the immobilizer control unit 17 with using the new red key5C, the engine start key 5A, 5B is rendered corresponding to the workmachine, thereby enabling the engine start key 5A, 5B to start theengine.

For example, in the case where the cryptographic codes are recorded inthe EEPROM 24 of the immobilizer control unit 17 as shown in FIG. 37,when the initialization code is identical with the code inputted by theinput means, the engine key 5 can be registered as the red key 5C. Whenthe engine key 5 in which the cryptographic code is [m] and thediscrimination code is blank as shown in the right table of FIG. 37 isinserted into the key cylinder 3, the cryptographic code of [m] of theengine key 5 is recorded (rewritten) in the memory area of the EEPROM 24of the immobilizer control unit 17 corresponding to the red key 5C asshown in the left table of FIG. 38, and the discrimination code of [v]of the red key 5C recorded in the ROM 25 of the immobilizer control unit17 is recorded in the EEPROM 11 of the inserted engine key 5 as shown inthe right table of FIG. 38. Thereafter, the cryptographic codes of theother keys other than the cryptographic code of [m] of the red key 5Cnewly recorded in the EEPROM 11 of the immobilizer control unit 17 arecleared as shown in the left table of FIG. 38.

Further, in the control mode of “keyless” of “initialization mode”, whenthe initialization code is identical with the input code, theinitialization is performed, and when the initialization code is notidentical with the input code, the initialization is renderedimpossible. Therefore, the initialization can be performed by knowingthe initialization code (personal identification code) recorded in theimmobilizer control unit 17.

However, in the control mode of “keyless” of “initialization mode”,since the initialization code is converted into the vehicle registrationnumber through the conversion function (step 240, step 241), theinitialization code for performing the initialization can not bedirectly known. Instead thereof, the vehicle registration number (dummyinitialization code) can be known by the display means 29 (step 242).

When the method of calculating the initialization code from the vehicleregistration number, that is, the conversion function provided in theimmobilizer control unit 17 is known, the initialization code can becalculated from the vehicle registration number.

That is, as is understood from step 241, since the vehicle registrationnumber is the value obtained by calculating the exclusive OR of theinitialization code and the calculation code, when the exclusive OR ofthe vehicle registration number and the calculation code is calculated,the value is restored to the initialization code.

For example, assuming the initialization code recorded in the ROM 25 ofthe immobilizer control unit 17 to be 5678 (hexadecimal number) and thecalculation code recorded in the ROM 25 of the immobilizer control unit17 to be 1234 (hexadecimal number), the exclusive OR of theinitialization code and the calculation code, that is, the vehicleregistration number is 444C (hexadecimal number), and the exclusive ORof the vehicle registration number 444C and the calculation code 1234(hexadecimal number) is 5678 (hexadecimal number), and this value isequal to the initialization code 5678 (hexadecimal number).

However, since the initialization code, the calculation code, therelation between the initialization code and the vehicle registrationnumber, and the like are previously recorded as the control program inthe immobilizer control unit 17, in general, even if only the vehicleregistration number is known, the initialization code (personalidentification code) can not be figured out from the vehicleregistration number.

Accordingly, similarly to the case of the engine starting code, theinitialization code can not be found, unless the user owning the workmachine makes inquiries to the manufacturer of the work machine(antitheft device 1) managing the vehicle registration numbers to learnthe initialization code (personal identification code) from themanufacturer, or unless the user learns the method of figuring out theinitialization code from the vehicle registration number from the workmachine manufacturer.

The method of figuring out the initialization code from the vehicleregistration number is similar to the foregoing method of figuring outthe engine starting code from the vehicle registration number (see FIG.34 and FIG. 35) except that the engine starting code is replaced by theinitialization code, and the description of the method of figuring outthe initialization code from the vehicle registration number will beomitted. Incidentally, in order to render the operation mode capable offiguring out both the engine starting code and the initialization codefrom the vehicle registration number, a manipulation to discriminatewhich of the engine starting code and the initialization code is to befigured out is incorporated in the procedure.

Next, the operation procedure of the control mode of “specialmanipulation” of “initialization mode” will be described by the use ofFIG. 41( a) and FIG. 41( b).

When the control mode of “special manipulation” of “initialization mode”starts, in step 250, the display part 29 displays “special manipulation”of “initialization mode” and ‘Please insert key’, and the procedureadvances to step 251.

In the 251, when the ignition switch 2 is rotated from the OFF positionto the ON position, it is judged that the engine key 3 is inserted, andthe procedure advances to step 252. When it is judged that the enginekey 3 is not inserted, the procedure returns to step 250.

Accordingly, when the control mode of “special manipulation” of“initialization mode” starts, until the engine key 5 is inserted intothe key cylinder 3, the display part 29 continues to display “specialmanipulation” of “initialization mode” and ‘Please insert key’ to urgethe insertion of the engine key 5 into the key cylinder 3.

In the step 252, the internal timer incorporated in the immobilizer CPU23 of the immobilizer control unit 17 is actuated.

In step 253, the immobilizer CPU 23 of the immobilizer control unit 17counts, using the signal form the key cylinder 3, how many times theignition switch 2 has been rotated from the OFF position to the ONposition (the number of times of ON-OFF rotation) after the internaltimer of the immobilizer CPU 23 of the immobilizer control unit 17 wasactuated (after the engine key 5 was inserted into the key cylinder 3),and it is judged whether or not the number of times of ON-OFF rotationof the ignition switch in the predetermined period of time T1 is Ntimes. When the number of times of ON-OFF rotation of the ignitionswitch 2 in the predetermined period of time T1 is N times, the internaltimer of the immobilizer CPU 23 of the immobilizer control unit 17 iscleared, and the procedure advances to next step 255, and otherwise, thenumber of times of rotation of the key is judged to be an invalid numberof times, and the procedure advances to step 254.

For example, assuming the predetermined period of time T1 to be tenseconds and the number of times of ON-OFF rotation to be ten times, inthe step 253, every turning motion of the ignition switch 2 from the OFFposition to the ON position is counted as one, and when the number oftimes of ON-OFF rotation in the predetermined period of time of tenseconds is ten times, the procedure advances to step 255, and when thenumber of times of ON-OFF rotation in the predetermined period of timeof ten seconds is other than ten times (for example, seven or twelvetimes), the procedure advances to step 254.

In the step 255, ‘Please proceed with next step’ is displayed on thedisplay part 29 for a predetermined period of time (several seconds).

In step 256, when the ignition switch 2 is rotated from the OFF positionto the ON position, it is judged that the engine key 3 is inserted, andthe procedure advances to step 257. When it is judged that the enginekey 3 is not inserted, the procedure returns to step 255.

In the step 257, the internal timer incorporated in the immobilizer CPU23 of the immobilizer control unit 17 is actuated.

In step 258, similarly to the above, the immobilizer CPU 23 of theimmobilizer control unit 17 counts how many times the ignition switch 2has been rotated by the key from the OFF position to the ON position(the number of times of ON-OFF rotation), and it is judged whether ornot the number of times of ON-OFF rotation of the key in a predeterminedperiod of time T2 is L times. When the number of times of ON-OFFrotation of the key in the predetermined period of time T2 is L times,the internal timer of the immobilizer CPU 23 of the immobilizer controlunit 17 is cleared, and the procedure advances to step 259, andotherwise, the number of times is judged to be an invalid number oftimes, and the procedure advances to step 254. In the step 254,‘Initialization can not be performed’ is displayed on the display part29 for a predetermined period of time, and the procedure returns to step250.

In the step 259, ‘Please insert key’ is displayed on the display part 29for a predetermined period of time, and the procedure advances to step260.

In the step 260, the discrimination code of the red key 5C of theimmobilizer control unit 17 is written into the EEPROM 11 of theinserted engine key 5 (for example, the rewritable engine key 5 havingthe cryptographic code).

In step 261, the cryptographic code of the engine key 5 is written intothe cryptographic code area of the corresponding area of the red key 5Cof the immobilizer control unit 17, thereby registering the engine key 5as the red key 5C.

In step 262, the cryptographic codes (the cryptographic codes of bluekey, yellow key, and green key) in the area other than the areacorresponding to the red key 5C of the immobilizer control unit 17 arecleared.

Accordingly, in the control mode of “special manipulation” of“initialization mode”, similarly to the control mode of “keyless” of“initialization mode”, since the engine key 5 having the ID code can beregistered as the red key 5C, and the cryptographic codes of the bluekey, the yellow key and the green key recorded in the immobilizercontrol unit 17 are cleared, the initialized state similar to FIG. 5 canbe obtained. When the yellow key 5B or the blue key 5A (engine startkey) is newly registered into the immobilizer control unit 17 with usingthe new red key 5C, the engine start key 5A, 5B is renderedcorresponding to the work machine, thereby enabling the engine start key5A, 5B to start the engine.

Further, in the control mode of “special manipulation” of“initialization mode”, the ID code recorded in the immobilizer controlunit 17 can be initialized by the special manipulation which isdifferent from operations for starting the engine (the ignition switchis successively rotated from the OFF position to the ON position withinthe predetermined period of time) with the engine key 5 (key capable ofrotating the ignition switch 2 from the OFF position to the ONposition).

The number of times N, L of ON-OFF rotation of the engine key 5 withinthe predetermined period of time is recorded in the immobilizer CPU 23of the immobilizer control unit 17, and the predetermined period of timeT1, T2 is also recorded in the immobilizer CPU 23 of the immobilizercontrol unit 17. Thus, in general, the number of times N, L of ON-OFFrotation and the predetermined period of time T1, T2 are not known evento the user owning the work machine. Unless the user owning the workmachine makes inquiries to the manufacturer to learn the number of timesN, L of ON-OFF rotation and the predetermined period of time T1, T2, orunless the user previously learns them from the manufacturer at the timeof purchasing the work machine or the like, the initialization can notbe performed.

For example, in the case where the user does not know the number oftimes N, L of ON-OFF rotation and the predetermined period of time T1,T2, the user owning the work machine makes a telephone call to themanufacturer, and notifies the user information (name, telephone number,birth date of the user owning the work machine, personal identificationnumber stated to the manufacturer at the time of purchasing the workmachine, and the like) to the manufacturer to prove that the user is acorrect user, so that the user is informed of the number of times N, Lof ON-OFF rotation and the predetermined period of time T1, T2, therebyallowing only the valid user to perform the initialization.

Further, since the user of the work machine can learn the number oftimes N, L of ON-OFF rotation and the predetermined period of time T1,T2 from the manufacturer also at the time of purchasing the workmachine, this special manipulation method can be known to only the user.

Incidentally, although the number of times N, L of ON-OFF rotation andthe predetermined period of time T1, T2 are known by making inquiries tothe manufacturer, the manufacturer may prepare a diagram showing thespecial manipulation method for the work machine and provide the rentalcompany or the personal user with the diagram, so that theinitialization can be performed with using the diagram showing thespecial manipulation only when the rental company or the personal userperforms the initialization by the special manipulation.

Since the special manipulation as described above is different fromoperations for starting engine and is complicated, it is difficult for aperson who intends to steal the machine to carry out the samemanipulation, and the initialization can be performed without ruiningthe antitheft function.

Further, by providing the two patterns of special manipulations such asthe step 253 and step 258, the antitheft function is further improved.Incidentally, the antitheft function can be improved by increasing thespecial manipulation as in the step 253 and step 258.

According to the above embodiment, through the operation procedure ofthe control mode of “blue key registration” in “each key registrationmode”, the new blue key 5A or the yellow key 5B can be formed from acommercially available engine key 5 or the like by the red key 5C or thegreen key (including both the master key and the slave key). Thus, inthe case where the user has lost the blue key 5A, replacement of thewhole antitheft device 1 is not required, since the blue key 5A capableof starting the engine of the work machine (vehicle) can be easily andnewly formed with using a commercially available engine key, and theengine can be started economically and conveniently while the antitheftdevice 1 is used as it is. Further, since the red key 5C or the greenkey 5D is required in order to form the new blue key 5A or the yellowkey 5B, it is difficult for a person other than the owner of the workmachine to form the blue key 5A for starting the engine, and theantitheft function of this antitheft system is not unexpectedly lost.

Further, since the blue key 5A or the yellow key 5B for starting theengine is a different key from the red key 5C or the green key 5D forallowing the rewriting or writing of the ID code, the keys can be easilyand conveniently managed.

Further, since the registered blue key 5A can not be registered as theblue key in the immobilizer control unit 17 of other work machines, theregistered blue key 5A can be used exclusively for starting the engineof one corresponding work machine. Accordingly, the blue key 5A can beconveniently used as the engine start key corresponding to only one workmachine. Since this blue key 5A can not be copied, stealing of themachine using a copy of the blue key 5A can also be prevented.

Through the operation of the control mode of “yellow key registration”in “each key registration mode”, the yellow key 5B (including both themaster key and the slave key) can be registered as the engine start keyinto the immobilizer control unit 17 of the work machine by the red key5C or the green key 5D (including both the master key and the slavekey). Further, since this registered yellow key 5B can also beregistered as the engine start key into the immobilizer control unit 17of other work machines, when the yellow key 5B is registered also intothe immobilizer control units 17 of other work machines, the engines ofplural work machines can be started by the master key or the slave keyof the one yellow key 5B.

Accordingly, for example, in the case where the owner of the rentalcompany having plural work machines checks those plural work machines,if the owner does not have the yellow key 5B, plural different enginekeys 5 (blue keys 5A) are required to start the engines of the workmachines, and at the time of check or the like, a key fitting to eachwork machine is required to be found from the plural keys, resulting incomplicated checking work or the like. However, as stated above, whenthe yellow key 5B is registered into the immobilizer control units 17 ofthe plural work machines, the engines of the plural work machines can bestarted by the master key or the slave key of the one yellow key 5B.Thus, the owner of the rental company has to have only one master key(or slave key) of the yellow key 5B as a spare key, and it is veryconvenient for the checking work or the like.

Through the operation procedure of the control mode of “green keyregistration” in “each key registration mode”, the green key 5D(including both the master key and the slave key) can be registered asthe allowance key into the immobilizer control unit 17 of the workmachine by the red key 5C. Further, since this registered green key 5Dcan also be registered as the allowance key into the immobilizer controlunits 17 of other work machines, when the green key 5D is registeredalso into the immobilizer control units 17 of other work machines, therewriting or writing of the ID code can be allowed in plural workmachines by the master key or the slave key of the one green key 5D.

Accordingly, for example, in the case where the owner of the rentalcompany having plural work machines has lost the blue keys 5A of thosework machines, if the owner does not have the green key 5D, since a newblue key 5A for starting the engine of each work machine is required tobe formed with using the red key 5C corresponding to each work machine,it is necessary to find out one red key 5C corresponding to each workmachine from plural keys for forming the new blue key 5A, which is avery complicated work. However, as stated above, where the green key 5Dis registered into the immobilizer control units 17 of plural workmachines, the blue keys 5A for starting the engines of the plural workmachines can be formed by the master key or the slave key of the onegreen key 5D. Thus, the owner of the rental company has to have only onemaster key (or slave key) of the green key 5D as the key for forming theblue key 5A, and this is very convenient for the work of forming bluekeys 5A or the like.

Through the operation procedure of the control mode of “yellow key copy”in “each key copy mode”, the slave key of the yellow key 5B can beformed by copying the master key of the yellow key 5B. Thus, forexample, as shown in FIG. 26, when the rental company of the workmachine lends the work machine, they keep the master key of the yellowkey 5B and lend the work machine with the slave key of the yellow key 5Bto a user, so that the rental company can start the engine of the workmachine by the master key of the yellow key 5B when the work machine isparked in the rental company, even if the user does not return the slavekey of the blue key 5A or the yellow key 5B, and this is convenient.Further, even if the rental company has plural parking places for theirwork machines, the engines of the work machines can be started by theslave key of the yellow key 5B in each of the parking places byproviding each parking place with the slave key of the copied yellow key5B, and this is convenient.

Through the operation procedure of the control mode of “green key copy”in “each key copy mode”, since the slave key of the green key 5D can beformed by copying the master key of the green key 5D, plural green keys5D (one master key and one or plural slave keys) to allow the rewritingor writing of the ID code can be formed for one work machine.

Accordingly, for example, in a nationwide rental company having pluralbranches each holding plural work machines, a work machine of a certainbranch is transferred to another branch. Thus, if the new blue key 5Acan only be formed by the red key 5C, in the case where the blue key 5Aof a work machine transferred to the another branch is lost, since onlyone red key 5C of work machine corresponds to that one work machine, andsince the red key 5C is generally kept in the branch which originallyheld the work machine, it is necessary to obtain the red key 5C from thebranch which originally held the work machine, and this is inconvenient.However, as shown in FIG. 26, if the master key of the green key 5D iskept in the branch which originally held the work machine and the slaveof the green key 5D is kept in another branch, when the blue key 5A ofthe work machine is lost in the another branch, the new blue key 5A canbe formed similarly to the red key 5C by the slave key of the green key5D of the branch without taking the trouble to obtain the red key 5Cfrom the branch which originally held the work machine, and the engineof the work machine can be started by this blue key 5A, which is veryconvenient.

Additional effects by the registration of the blue key 5A, the copy ofthe yellow key 5B, the copy of green key 5D, and the like are as shownin FIG. 26.

The display part 29 variably displaying the manipulation for preventingtheft is controlled by the immobilizer control unit 17 so that themanipulation to register the start key (the blue key 5A, the yellow key5B), the manipulation to register the allowance key (green key 5D), andthe manipulation to copy the key (the yellow key 5B, the green key 5D)are sequentially variably displayed. Thus, when the blue key 5A, theyellow key 5B and the green key 5D are registered, or when the yellowkey 5B and green key 5D are copied, since those manipulations aresequentially displayed on the display part 29, the manipulation of theregistration of the key and the manipulation of the key copy can besmoothly and certainly performed without mistakes.

Further, since each time a manipulation is performed, the display part29 sequentially variably displays a manipulation to be performed next, amanipulation, as a manipulation to prevent theft, to be performed nextcan be easily and certainly known without errors, and the manipulationto prevent theft can be performed more smoothly and easily. Furthermore,since the display part 29 sequentially variably displays the controlmode of the immobilizer control unit 17, it is possible to certainlyknow in which control mode the current manipulation is being performed,and the manipulations in the respective control modes to prevent theftcan be smoothly performed.

Through the operation procedure of the control mode of “red key use” or“special manipulation” in “vehicle resale mode”, the cryptographic codeof the yellow key 5B or the green key 5D recorded in the EEPROM 24 ofthe immobilizer control unit 17 of the work machine can be deleted(cleared). For example, in the case where a rental company E distributesplural green keys 5D of a work machine G to plural branches and each ofthe branches keeps the green key 5D, when the work machine G is resoldto a rental company F, the rental company E (seller) deletes the ID codeof the green key 5D recorded in the immobilizer control unit 17 of thework machine G through “red key use mode” or “special manipulation” modebefore the work machine G is resold to the rental company F. As aresult, after the work machine G is resold to the rental company F, anew blue key 5A or yellow key 5B cannot be recorded into the workmachine G with using the green key 5D of the work machine G owned by therental company E before the resale.

Accordingly, even if the owner of the work machine G changes, theantitheft system can be used as it is, and it is not necessary toreplace the antitheft system for the resale.

With the operation procedure of the control mode of “keyless” or“special manipulation” in “emergency start mode”, even in the case wherethe engine start key 5A, 5B is lost, or the allowance key 5C, 5D islost, the engine can be started without ruining the antitheft function.Thus, for example, as shown in FIG. 26, when a work machine (C-2) of a Cbranch of a rental company A is lent and is transferred to a D branch,if the blue key 5A of the work machine (C-2) has been lost and the greenkey 5D corresponding to the work machine (C-2) in the D branch has beenlost, that is, in the case where the new blue key 5A can not be formedby the green key 5D, the work machine (C-2) can be driven withoutobtaining the red key 5C of the work machine (C-2) from the C branch,which is convenient.

Further, even in the case where the antenna 15 provided in the keycylinder 3 fails, and the ID code collation can not be performed betweenthe engine key 5 and the immobilizer control unit 17, the engine can bestarted without ruining the antitheft function.

Through the operation procedure of the control mode of “keyless” or“special manipulation” in “initialization mode”, the cryptographic codesof the blue key 5A, the yellow key 5B and the green key 5D recorded inthe EEPROM 24 of the immobilizer control unit 17 can be cleared, and thered key 5C is newly registered. Thus, for example, since the blue key5A, the yellow key 5B and the green key 5D can be newly registered withusing the new red key 5C, the correspondence relation of the blue key5A, the yellow key 5B, the red key 5C, and the green key 5D newlyregistered in the immobilizer control unit 17 (antitheft device 1) withrespect to the antitheft device 1 is organized, and without searchingthe engine key 5 corresponding to the work machine, the engine can bestarted by the newly registered engine start key 5A, 5B, and copies ofthe engine start key 5A, 5B can be formed by the newly registeredallowance key 5C, 5D.

Further, in the case where the red key 5C is lost, it is possible thatthe engine start key 5A, 5B is formed with using the lost red key 5C.However, since the ID code of the red key 5C recorded in the immobilizercontrol unit 17 is rewritten by the ID code of the newly recorded redkey 5C through the operation procedure of the control mode of“initialization mode”, registration of another key with using the lostred key 5C is prevented, and even in the case where the red key 5C islost, it is not necessary to replace the antitheft device 1 with a newone, and the antitheft function can be ensured.

FIG. 40 shows another embodiment, in which conditions under which thecontrol mode shown in FIG. 8 is started are changed. When the red key 5Cis inserted into the key cylinder 3, the ID code of the red key 5C iscollated with the ID code recorded in the immobilizer control unit 17,and when the result of the collation is affirmative, the control modewhich allows the start key registration function provided in theimmobilizer control unit 17 to perform is started. Other constructionsare the same as those of the foregoing embodiment.

Next, the procedure for starting the control mode will be described withreference to a flowchart of FIG. 40. In step 111, it is judged whetheror not the engine key 5 is inserted into the key cylinder 3, and when itis judged that the engine key 5 is inserted, the procedure advances tostep 112, and when it is judged that the engine key 5 is not inserted,the procedure returns to step 111.

Accordingly, in the step 111, the judgment of whether or not the enginekey 5 is inserted into the key cylinder 3 is repeated until the enginekey 5 (the red key 5C) is inserted into the key cylinder 3.

In the step 112, it is judged whether or not the discrimination code ofthe engine key 5 inserted into the key cylinder 3 is identical with thediscrimination code of the red key 5C. When it is identical with thediscrimination code of the red key 5C, the procedure advances to step114, and when it is not identical with the discrimination code of thered key 5C, the procedure returns to step 111.

In the step 114, it is judged whether or not the cryptographic code ofthe engine key 5 inserted into the key cylinder 3 is identical with thecryptographic code recorded in the immobilizer control unit 17. When thecryptographic codes are identical, the procedure advances to step 115,and when the cryptographic codes are not identical, ‘Key does notcoincide’ is displayed on the display part 29, and the procedure returnsto step 111.

Accordingly, when the red key 5C other than the registered red key 5C isinserted into the key cylinder 3, after it is notified that theunregistered erroneous red key 5C has been inserted into the keycylinder 3 by displaying ‘Key does not coincide’ on the display part 29,the judgment of whether or not the engine key 5 is inserted into the keycylinder 3 is repeated.

When the cryptographic codes are judged to be identical in the step 114,the control mode for preventing theft, as shown in FIG. 8, starts withdisplaying “each key registration mode” of the main menu in the step115. The subsequent operation procedure is the same as the case of theformer embodiment, and each time the third switch 33 is pressed, thecontrol mode of the main menu is sequentially changed from “eachregistration mode” to “each key copy mode”, “vehicle resale mode”,“emergency start mode”, and “initialization mode”. When the third switch33 is further pressed, the control mode returns to “each keyregistration mode”, and hereinafter, each time the third switch 33 ispressed, the changeover of the control mode of the main menu isrepeated. Further operations for changing control modes of submenu ineach control mode, the operation procedure of the each key registrationmode, the operation procedure of the each key copy mode, the operationprocedure of the wheel resale mode, the operation procedure of theemergency start mode, and the operation procedure of the initializationmode are also the same as those of the former embodiment.

According to this embodiment, for operating the control mode forpreventing theft as shown in FIG. 8, a complicated manipulation in whichwhile pressing the third switch 33 of the display device 18, the enginekey 5 is inserted into the key cylinder 3, and the main switch 2 ismanipulated from the OFF position (OFF) to the ON position (ON), as inthe case of the foregoing embodiment, is not required. When the red key5C recorded in the immobilizer control unit 17 is simply inserted intothe key cylinder 3, the control mode for preventing theft is started,and the troublesomeness of the manipulation for starting the controlmode is eliminated.

Incidentally, in the embodiment of FIG. 40, the control mode starts whenthe red key 5C recorded in the immobilizer control unit 17 is insertedinto the key cylinder 3. Alternatively, the control mode may be arrangedto start when the green key 5D (both the master key and the slave key orone of them) recorded in the immobilizer control unit 17 is insertedinto the key cylinder 3, or the control mode may be arranged to startwhen one of the red key 5C recorded in the immobilizer control unit 17and the green key 5D (both the master key and the slave key or one ofthem) recorded in the immobilizer control unit 17 is inserted into thekey cylinder 3.

FIG. 41( a), FIG. 41( b), FIG. 42( a) and FIG. 42( b) show yet anotherembodiment, in which conditions for starting the control mode shown inFIG. 8 are changed, and conditions for starting the each keyregistration mode and the each key copy mode in the control mode arechanged. In this embodiment, the master key of the yellow key 5B is usedonly for forming (copying) the slave key of the yellow key 5B, and isnot registered in the immobilizer control unit 17, and the engine cannot be started by the master key of the yellow key 5B. Further, themaster key of the green key 5D is used only for forming (copying) theslave key of the green key 5D, and is not registered in the immobilizercontrol unit 17, and registration of the blue key 5A and registration ofthe yellow key 5B can not be performed by the master key of the greenkey 5D.

That is, when the red key 5C or the slave key of the green key 5D isinserted into the key cylinder 3, the ID code of the red key 5C or slavekey of the green key 5D is collated with the ID code recorded in theimmobilizer control unit 17. When the result of the collation isaffirmative, the control mode which allows the start key registrationfunction to be operated is actuated. When the blue key 5A (the enginekey 5 other than the red key 5C, the yellow key 5B and the green key 5D)is inserted into the key cylinder 3 without interruption after the redkey 5C or the slave of the green key 5D is inserted into the keycylinder 3, the control mode of “blue key registration” of “each keyregistration mode” starts. Then, the ID code of the engine key 5 isrendered corresponding to the ID code of the immobilizer control unit 17by the start key registration function provided in the immobilizercontrol unit 17 so that the engine key 5 serves as the blue key 5A. Morespecifically, the memory area, corresponding to the discrimination codeof the blue key 5A, of the EEPROM 24 of the immobilizer control unit 17is cleared, and the cryptographic code of the engine key 5 is writteninto this area, while the discrimination code of the blue key recordedin the ROM 25 of the immobilizer control unit 17 is written into theengine key 5, so that identical pairs of cryptographic code anddiscrimination code are recorded in the engine key 5 and the immobilizercontrol unit 17. As a result, the ID code of the engine key 5 isrendered corresponding to the ID code of the immobilizer control unit 17so that the engine key 5 serves as the blue key 5A. Further, at thistime, overwriting of the discrimination code of the registered blue key5A is rendered impossible, and registration of the cryptographic code ofthe blue key 5A is rendered impossible so that this blue key 5A can notbe registered as the blue key into the immobilizer control unit ofanother work machine.

When the slave key of the yellow key 5B (slave key of the yellow key 5Bin which the cryptographic code and the discrimination code are recordedand which does not serve as the engine start key) is inserted into thekey cylinder 3 without interruption after the red key 5C or the slavekey of the green key 5D is inserted into the key cylinder 3, theimmobilizer control unit 17 enters into the control mode of “yellow keyregistration” of “each key registration”. Then, the ID code of the slavekey of the yellow key 5B is rendered corresponding to the ID code of theimmobilizer control unit 17 by the start key registration functionprovided in the immobilizer control unit 17 so that the slave key of theyellow key 5B serves as the yellow key 5B. More specifically, thecryptographic code of the slave key of the yellow key 5B which does notfunction as the engine start key is written into the memory area,corresponding to the discrimination code of the yellow key 5B, of theEEPROM 24 of the immobilizer control unit 17, so that identical pairs ofcryptographic code and discrimination code are recorded in the slave keyof the yellow key 5B and the immobilizer control unit 17. As a result,the ID code of the slave key of the yellow key 5B is renderedcorresponding to the ID code of the immobilizer control unit 17, so thatthe engine key 5 serves as the yellow key 5B. Further, at this time, inorder that the slave key of the registered yellow key 5B can beregistered as the yellow key into the immobilizer control unit 17 ofanother work machine, registration of the cryptographic code of theyellow key 5B is not rendered impossible, but is made to remainpossible.

When the slave key of the green key 5D (the slave key of the green key5D in which the cryptographic code and the discrimination code arerecorded and which does not serve as the allowance key) is inserted intothe key cylinder 3 without interruption after the red key 5C or theslave of the green key 5D is inserted into the key cylinder 3, thecontrol mode of “green key registration” of “each key registration mode”starts. Then, the ID code of the slave key of the green key 5D isrendered corresponding to the ID code of the immobilizer control unit 17by the allowance key registration function provided in the immobilizercontrol unit 17 so that the engine key 5 serves as the green key 5D.More specifically, the cryptographic code of the slave key of the greenkey 5D is written into the memory area, corresponding to thediscrimination code of the green key 5D, of the EEPROM 24 of theimmobilizer control unit 17, so that identical pairs of cryptographiccode and discrimination code are recorded in the slave key of the greenkey 5D and the immobilizer control unit 17. As a result, the ID code ofthe slave key of the green key 5D is rendered corresponding to the IDcode of the immobilizer control unit 17, so that the engine key 5 servesas the green key 5D. Further, at this time, in order that the slave keyof the registered green key 5D can be registered as the green key intothe immobilizer control unit of another work machine, registration ofthe cryptographic code of the green key 5D is not rendered impossible,but is made to remain possible.

When the master key of the green key 5D is inserted into the keycylinder 3, the control mode which allows the allowance key copyfunction to be operated is actuated, and the control mode of “green keycopy” of “each key copy mode” starts. Then, the ID code of the masterkey of the green key 5D is allowed to be written into another engine key5 by the allowance key copy function provided in the immobilizer controlunit 17 so that the engine key serves as the allowance key. Morespecifically, the ID code (only the cryptographic code) of the masterkey of the green key 5D is written into the RAM 26 of the immobilizercontrol unit 17, and then, when another engine key 5 is inserted intothe key cylinder 3, the cryptographic code of the master key written inthe immobilizer control unit 17 and the discrimination code denoting theslave key of the green key 5D are written into the EEPROM 11 of theengine key 5. As a result, identical pairs of cryptographic code anddiscrimination code are recorded in the engine key 5 and the immobilizercontrol unit 17, so that the ID code of the engine key 5 is renderedcorresponding to the ID code of the immobilizer control unit 17, and themaster key of the green key 5D is copied into the engine key 5 as theslave key of the green key 5D.

When the master key of the yellow key 5B is inserted into the keycylinder 3, the control mode which allows the start key copy function tobe operated is actuated, and the control mode of “yellow key copy” of“each key copy mode” starts. Then, the ID code of the master key of theyellow key 5B is allowed to be written into the another engine key 5 bythe start key copy function provided in the immobilizer control unit 17so that the engine key serves as the engine start key. Morespecifically, the ID code (only the cryptographic code) of the masterkey of the yellow key 5B is written into the RAM 26 of the immobilizercontrol unit 17, and then, when another engine key 5 is inserted intothe key cylinder 3, the cryptographic code of the master key written inthe immobilizer control unit 17 and the discrimination code denoting theslave key of the yellow key 5B are written into the EEPROM 11. As aresult, identical pairs of cryptographic code and discrimination codeare recorded in the engine key 5 and the immobilizer control unit 17, sothat the ID code of the engine key 5 is rendered corresponding to the IDcode of the immobilizer control unit 17, and the master key of theyellow key 5B is copied into the engine key 5 as the slave key of theyellow key 5B.

The other constructions are the same as those of the foregoingembodiment.

Next, the operation procedure of the control mode will be described withreference to flowcharts of FIG. 41( a), FIG. 41( b), FIG. 42( a) andFIG. 42( b).

In step 121, it is judged whether or not the engine key 5 is insertedinto the key cylinder 3, and when it is judged that the engine key 5 isinserted, the procedure advances to step 122, and when it is judged thatthe engine key 5 is not inserted, the procedure returns to step 121.

In the step 122, it is judged whether or not the discrimination code ofthe engine key 5 inserted into the key cylinder 3 is identical with thediscrimination code of the red key 5C or the slave key of the green key5D. When it is identical with the discrimination code of the red key 5Cor the slave key of the green key 5D, the procedure advances to step124, and when it is not identical with the discrimination code of thered key 5C or the slave key of the green key 5D, the procedure advancesto step 123.

In the step 124, it is judged whether or not the cryptographic code ofthe red key 5C or the slave key of the green key 5D inserted into thekey cylinder 3 is identical with the cryptographic code recorded in theimmobilizer control unit 17. When the cryptographic codes are identical,the procedure advances to step 126, and when the discrimination codesare not identical, the procedure advances to step 125 with displaying‘Key does not coincide’ on the display part 29, and the procedurereturns to step 121.

Accordingly, when the unregistered red key 5C or the slave key of thegreen key 5D is inserted into the key cylinder 3, it is notified thatthe unregistered erroneous red key 5C or the slave key of the green key5D has been inserted into the key cylinder 3 by displaying ‘Key does notcoincide’ on the display part 29.

In the step 124, when the cryptographic codes are judged to beidentical, the control mode is actuated in step 126. Then, in step 127,‘Please insert key’ is displayed on the display part 29 (until a new keyis inserted into the key cylinder 3) and when the new key is insertedinto the key cylinder 3, the procedure advances to step 128.

In the step 128, it is judged whether or not the engine key 5 insertedinto the key cylinder 3 is the blue key 5A (the engine key 5 other thanthe red key 5C, the yellow key 5B and the green key 5D) which can beregistered. In this judgment, only when the cryptographic code isrecorded in the inserted engine key 5, and the memory area of thediscrimination code of the engine key 5 is blank or the discriminationcode of the blue key is recorded in the memory area of thediscrimination code, the engine key is judged to be the blue key 5Awhich can be registered, and the procedure advances to step 132. Whenthe discrimination code of the engine key 5 inserted into the keycylinder 3 is other than that of the blue key 5A, namely, thediscrimination code of the master key of the yellow key 5B, thediscrimination code of the slave key of the yellow key 5B, thediscrimination code of the master key of the green key 5D, and thediscrimination code of the slave of the green key 5D, or the engine keyis the blank key (the engine key 5 in which the cryptographic code isnot recorded), the engine key is judged not to be the blue key 5A whichcan be registered, and the procedure advances to step 129.

Accordingly, only the engine key 5 in which the cryptographic code isrecorded and the discrimination code other than the blue key 5A is notrecorded is judged to be registrable as the blue key, and the engine key5 other than this is not registered.

In the step 129, it is judged whether or not the engine key 5 insertedinto the key cylinder 3 is the slave key of the yellow key 5B. When thecryptographic code is recorded in the inserted engine key 5 and thediscrimination code of the slave key of the yellow key 5B is recorded inthe memory area of the discrimination code of the engine key 5, theengine key is judged to be the slave key of the yellow key 5B, and theprocedure advances to step 135, and otherwise, the engine key is judgednot to be the slave key of the yellow key 5B, and the procedure advancesto step 130.

Accordingly, only the slave key of the yellow key 5B is registered asthe yellow key 5B, and the master key of the yellow key 5B and the otherkeys are not registered.

In the step 130, it is judged whether or not the engine key 5 insertedinto the key cylinder 3 is the slave key of the green key 5D. In thisjudgment, when the cryptographic code is recorded in the inserted enginekey 5 and the discrimination code of the slave key of the green key 5Dis recorded in the memory area of the discrimination code of the enginekey 5, the engine key is judged to be the slave key of the green key 5D,and the procedure advances to step 137. When the discrimination code ofthe engine key 5 inserted into the key cylinder 3 is other than that ofthe slave key of the green key, the discrimination code is not recorded,or the cryptographic code is not recorded, the engine key is judged notto be the slave key of the green key 5D, and the procedure advances tostep 131.

Accordingly, only the slave key of the green key 5D is registered as thegreen key 5D, and the master key of the green key 5D and the other keysare not registered.

When the procedure advances from step 130 to step 131, in the step 131,‘This key can not be registered’ is displayed on the display part 29,and the procedure returns to step 127. Thereafter, the operation isrepeated for a predetermined period of time through the loop of step127, step 128, step 129, step 130 and step 131, and if none of the bluekey 5A, the slave key of the yellow key 5B and the slave key of thegreen key 5D is inserted into the key cylinder 3 during thepredetermined period of time, the procedure returns to step 121 oradvances to END.

Accordingly, in the case where the engine key 5 inserted into the keycylinder 3 is not the blue key 5A, the slave key of the yellow key 5B,or the slave key of the green key 5D, the display of ‘Please insert key’and the display of ‘This key can not be registered’ are alternatelyrepeated, and when the blue key 5A, the slave key of the yellow key 5B,or the slave key of the green key 5D is inserted during the abovedisplay, the registration of the blue key 5A, the slave key of theyellow key 5B, or the slave key of the green key 5D that will bedescribed below is performed.

In step 132, after the memory area of the cryptographic code,corresponding to the blue key 5A, of the EEPROM 24 of the immobilizercontrol unit 17 is cleared (see FIG. 11), the cryptographic code of theengine key 5 inserted into the key cylinder 3 is written into the memoryarea, corresponding to the blue key, of the EEPROM 24. Instep 133, thediscrimination code of the blue key is written into the EEPROM 11 of theinserted engine key 5, overwriting of the discrimination code of theregistered engine key 5 (the blue key 5A) is rendered impossible, andregistration of the cryptographic code is rendered impossible. Instep134, “Blue key is registered” is displayed on the display part 29, andthe registration operation of the blue key 5A ends.

Accordingly, among engine keys 5, with respect to the engine key 5 inwhich only the cryptographic code is recorded and the discriminationcode is not recorded, or the engine key 5 (unregistered blue key 5A) inwhich the cryptographic code is recorded and the discrimination code ofthe blue key is recorded, the ID code of the engine key 5 corresponds tothe ID code of the immobilizer control unit 17, so that the blue key isregistered to serve as the engine start key, a new blue key 5A isformed, and the engine can be started by this blue key 5A. In thisoperation, since the overwriting of the discrimination code of the bluekey 5A is rendered impossible, this blue key 5A can not be changed tothe yellow key 5B or the other key after this operation. Further, sincethe registration of the cryptographic code of the blue key 5A isimpossible, this blue key 5A can not be registered as the blue key intothe immobilizer control unit 17 of another work machine after thisoperation, and accordingly, this blue key 5A can be used only forstarting the engine of the work machine corresponding to this key.

In step 135, the cryptographic code of the engine key 5 inserted intothe key cylinder 3 is written into the memory area, corresponding to theslave key of the yellow key 5B, in the EEPROM 24 of the immobilizercontrol unit 17, and in step 136, ‘Yellow key has been registered’ isdisplayed on the display part 29, and the registration operation of theslave key of the yellow key 5B ends.

Accordingly, among engine keys 5, with respect to the key in which thecryptographic code is recorded and the discrimination code of the slavekey of the yellow key is recorded, the ID code of the engine key 5corresponds to the ID code of the immobilizer control unit 17, so thatthe slave key of the yellow key is registered to serve as the enginestart key, and the engine can be started by this slave key of the yellowkey 5B.

In step 137, the cryptographic code of the engine key 5 inserted intothe key cylinder 3 is written into the memory area, corresponding to themaster key of the green key 5D, in the EEPROM 24 of the immobilizercontrol unit 17, and at this time, the same cryptographic code issimultaneously written into the memory area, corresponding to the slavekey of the green key 5D, in the EEPROM 24, and the registrationoperation of the green key 5D ends.

Accordingly, among engine keys 5, with respect to the key in which thecryptographic code is recorded and the discrimination code of the slavekey of the green key is recorded, the ID code of the engine key 5corresponds to the ID code of the immobilizer control unit 17, so thatthe green key is registered to serve as the allowance key, therebyenabling this slave key of the green key 5D to allow rewriting orwriting of the ID code.

In step 123, it is judged whether or not the discrimination code of theengine key 5 inserted into the key cylinder 3 is identical with thediscrimination code of the master key of the green key 5D or the masterkey of the yellow key 5B. When it is identical with the discriminationcode of the master key of the green key 5D or the master key of theyellow key 5B, the procedure advances to step 141 of FIG. 44, and whenit is not identical with the discrimination code of the master key ofthe green key 5D or the master key of the yellow key 5B, the procedurereturns to step 121.

In the step 141, the control mode is started, and in step 142, it isjudged whether or not the engine key 5 inserted into the key cylinder 3is the master key of the yellow key 5B. When it is the master key of theyellow key 5B, the procedure advances to step 142, and when it is notthe master key of the yellow key 5B, the procedure advances to step 143.In the step 143, it is judged whether or not the engine key 5 insertedinto the key cylinder 3 is the master key of the green key 5D, and whenit is the master key of the green key 5D, the procedure advances to step151.

Accordingly, when the master key of the yellow key 5B is inserted intothe key cylinder 3, the control mode is immediately actuated, and thecontrol mode of “green key copy” of “each key copy mode” starts. Whenthe master key of the green key 5D is inserted into the key cylinder 3,the control mode is immediately actuated, and the control mode of“yellow key copy” of “each key copy mode” starts.

When the procedure advances from step 142 to step 144, in the step 144,the cryptographic code of the master key of the yellow key 5B is writteninto the RAM 26 of the immobilizer control unit 17, and in step 145,‘Please insert key for copy’ is displayed on the display part 29 (untila new key is inserted into the key cylinder 3), and the procedureadvances to step 146.

In the step 146, it is judged whether or not the inserted key iswritable. In this judgment, in the case where the discrimination code ofthe red key 5C, the discrimination code of the master key of the yellowkey 5B or the discrimination code of the master key of the green key 5Dis not recorded in the memory area of the discrimination code of theinserted engine key 5, that is, when the memory areas of thecryptographic code and the discrimination code are blank (blank key), orthe cryptographic code is recorded and the memory area of thediscrimination code is blank, the key is judged to be registrable, andthe procedure advances to step 148. In the case where the discriminationcode of the red key 5C, the discrimination code of the master key of theyellow key 5B, or the discrimination code of the master key of the greenkey 5D is recorded as the discrimination code of the engine key 5inserted into the key cylinder 3, the key is judged to be unregistrable,and the procedure advances to step 147. In the step 147, ‘This key cannot be used for copy’ is displayed on the display part 29 for apredetermined period of time (several seconds), and the procedurereturns to step 145. However, as to whether or not the inserted key iswritable, with respect to the blue key 5A, the blue key 5A having beenregistered in the immobilizer control unit 17 is judged to beunwritable, while the unregistered blue key 5A is judged to be writable.

Accordingly, when the unrewritable or unwritable engine key 5 isinserted into the key cylinder 3, after it is notified that theunrewritable red key 5C, master key of the yellow key 5B, master key ofthe green key 5D, or registered blue key 5A has been erroneouslyinserted into the key cylinder 3 by displaying ‘This key can not be usedfor copy’ on the display part 29, the insertion of a key for copy intothe key cylinder 3 is urged again.

In the step 146, when the inserted key is judged to be writable, theprocedure advances to step 148. In the step 148, the discrimination codeof the slave key of the yellow key and the cryptographic code identicalwith the cryptographic code of the master key of the yellow key 5B arewritten into the EEPROM 11 of the engine key 5 for copy, or the datarecorded in the EEPROM 11 of the engine key 5 for copy is rewritten tothe discrimination code of the slave key of the yellow key and thecryptographic code identical with the cryptographic code of the masterkey of the yellow key 5B, whereby the ID code of the engine key 5 isrendered corresponding to the ID code of the immobilizer control unit 17so that the engine key 5 serves as the slave key of the yellow key 5B,and as a result, the master key of the yellow key 5B is copied into theengine key 5, and the slave key of the yellow key 5B is formed.

In step 150, it is judged whether or not a further copy of the yellowkey is to be formed, and when it is judged that another copy of theyellow key is to be formed, the procedure returns to step 145, and thenext coping procedure of the yellow key is performed. The judgment as towhether or not the yellow key is to be copied is made according to, forexample, whether or not the first switch 31 is operated to be ON withina predetermined period of time. When the first switch 31 is operated tobe ON, it is judged that the copying procedure of the yellow key 5B isto be performed, and the procedure returns to step 145. When the firstswitch 31 is not operated to be ON within the predetermined period oftime, it is judged that the copying procedure of the yellow key is notto be performed, and the copy operation of the yellow key 5B ends.Accordingly, the yellow key can be continuously copied with respect toplural engine keys 5.

Incidentally, the operations in the steps 144 to 150 are similar to theoperations in the steps 65 to 70 of FIG. 19( a) and FIG. 19( b) of theforegoing embodiment.

When the procedure advances from step 143 to step 151, in the step 151,the cryptographic code of the master key of the green key 5D is writteninto the RAM 26 of the immobilizer control unit 17. In step 152, ‘Pleaseinsert key for copy’ is displayed on the display part 29 (until a newkey is inserted into the key cylinder 3), and the procedure advances tostep 153.

In the step 87, it is judged whether or not the inserted key iswritable. In this judgment, in the case where the discrimination code ofthe red key 5C, the discrimination code of the master key of the yellowkey 5B, or the discrimination code of the master key of the green key 5Dis not recorded in the memory area of the discrimination code of theinserted engine key 5, that is, where the memory areas of thecryptographic code and the discrimination code are blank (blank key), orthe cryptographic code is recorded and the memory area of thediscrimination code is blank, the key is judged to be writable, and theprocedure advances to step 155. In the case where the discriminationcode of the red key 5C, the discrimination code of the master key of theyellow key 5B, or the discrimination code of the master key of the greenkey 5D is recorded as the discrimination code of the engine key 5inserted into the key cylinder 3, the key is judged to be unwritable,and the procedure advances to step 154. In the step 154, ‘This key cannot be used for copy’ is displayed on the display part 29 for apredetermined period of time (several seconds), and the procedurereturns to step 152. However, as to whether or not the inserted key iswritable, with respect to the blue key 5A, the blue key 5A having beenregistered in the immobilizer control unit 17 is judged to beunwritable, while the unregistered blue key 5A is judged to be writable.

Accordingly, when the unrewritable or unwritable engine key 5 isinserted into the key cylinder 3, after it is notified that theunrewritable red key 5C, master key of the yellow key 5B, master key ofthe green key 5D, or registered blue key 5A has been erroneouslyinserted into the key cylinder 3 by displaying ‘This key can not be usedfor copy’ on the display part 29, the insertion of a key for copy intothe key cylinder 3 is urged again.

In the step 153, when the inserted key is judged to be writable, theprocedure advances to step 155. In the step 155, the discrimination codeof the slave key of the green key 5D and the cryptographic codeidentical with the cryptographic code of the master key of the green key5D are written into the EEPROM 11 of the engine key 5 for copy, or thedata recorded in the EEPROM 11 of the engine key 5 for copy is rewrittento the discrimination code of the slave key of the green key 5D and thecryptographic code identical with the cryptographic code of the masterkey of the green key 5D, whereby the ID code of the engine key 5 isrendered corresponding to the ID code of the immobilizer control unit 17so that the engine key 5 serves as the slave key of the green key 5D,and as a result, the master key of the green key 5D is copied into theengine key 5, and the slave key of the green key 5D is formed.

In step 157, it is judged whether or not a further copy of the green keyis to be formed, and when it is judged that another copy of the greenkey is to be formed, the procedure returns to step 152, and the nextcoping procedure of the green key is performed. The judgment as towhether or not the copy of the green key is to be formed is madeaccording to, for example, whether or not the first switch 31 isoperated to be ON within a predetermined period of time. When the firstswitch 31 is operated to be ON, it is judged that the copying procedureof the green key 5D is to be performed, and the procedure returns tostep 152. When the first switch 31 is not operated to be ON within thepredetermined period of time, it is judged that the copying procedure ofthe green key is not to be performed, and the copy operation of thegreen key ends. Accordingly, the green key can be continuously copiedwith respect to plural engine keys 5.

Incidentally, the operations in the steps 151 to 157 are similar to theoperations in the step 85 to 90 of FIG. 22( a) and FIG. 22( b) of theforegoing embodiment.

Incidentally, in the embodiment of FIG. 41( a), FIG. 41( b), FIG. 42( a)and FIG. 42( b), although the description of the operations of thecontrol modes of “vehicle resale mode”, “emergency start mode” and“initialization mode” are omitted, the respective operations of thesecontrol modes of “vehicle resale mode”, “emergency start mode” and“initialization mode” can be arranged to start by special specificmanipulations or the like, so that the respective operations may beperformed through the same steps as the foregoing embodiment.

Further, in the embodiment of FIG. 41( a), FIG. 41( b), FIG. 42( a) andFIG. 42( b), the starting of the engine is performed with using the bluekey 5A or the slave key of the yellow key 5B. Although the descriptionof the engine starting operation is omitted, it is performed by the sameoperation as the engine starting operation shown in the flowcharts ofFIG. 25( a) and FIG. 25( b).

According to the above embodiment, the effects similar to the embodimentof FIGS. 1 to 39( b) are obtained. Further, since the control mode inwhich the start key registration function is actuated, the control modein which the allowance key copy function is actuated, or the controlmode in which the start key copy function actuated is started byinserting the red key 5C, the slave key of the green key 5D, the masterkey of the green key 5D, or the master key of the yellow key 5B into thekey cylinder 3, similarly to the embodiment of FIG. 40, the troublesomemanipulations to start the control mode is eliminated. Furthermore,since a desired one of the control mode of “blue key registration”, thecontrol mode of “yellow key registration”, the control mode of “greenkey registration”, the control mode of “yellow key copy”, and thecontrol mode of “green key copy” is started according to the kind of thekey (the red key 5C, the slave key of the green key 5D, the master keyof the green key 5D, or the master key of the yellow key 5B) insertedinto the key cylinder 3, the manipulations to change the mode (menuselection) in the control mode is not required, thereby considerablysimplifying the manipulations, so that the key registration and key copycan be performed in a short period of time.

Incidentally, in the above embodiments, although two kinds of enginestart keys of the blue key 5A and the yellow key 5B are provided as theengine start key, the blue key 5A may be solely provided as the enginestart key without the yellow key 5B, or the yellow key 5B may be solelyprovided as the engine start key without the blue key 5A.

Further, in the above embodiments, although two kinds of allowance keysof the red key 5C and the green key 5D are provided as the allowance keyto allow the rewriting or writing of the ID code, the red key 5C may besolely provided as the allowance key without the green key 5D, or thegreen key 5D may be solely provided as the allowance key without the redkey 5C.

Further, in the above embodiments, as the allowance tool to allow therewriting or writing of the ID code, the allowance key 5C, 5Dconstructed of the engine key 5 which can be inserted into the keycylinder 3 is used. However, since the allowance tool can not start theengine, it is not required to be constructed of the engine key 5 whichcan be inserted into the key cylinder 3. Accordingly, the allowance toolto allow the rewriting or writing of the ID code may be constructed of,for example, a member which has only a portion corresponding to the headportion of the engine key in which the transponder chip 9 is embedded,but does not have a key portion to be inserted into the key cylinder 3.

Further, in the above embodiments, although the cryptographic code andthe discrimination code are separately used as the ID codes of theengine key and the immobilizer control unit 17, the ID code may consistof only one kind of cryptographic code or the like.

Further, in the above embodiments, although the yellow key 5B and thegreen key 5D each consists of the master key and the slave key which aredistinguished by the discrimination code, the distinction between themaster key and the slave key of the yellow key 5B may be eliminated byallotting an identical discrimination code, or the distinction betweenthe master key and the slave key of the green key 5D may be eliminatedby allotting an identical discrimination code.

Further, in the control mode of “vehicle resale mode” of the aboveembodiment, although the ID codes of the yellow key 5B and the green key5D recorded in the immobilizer control unit 17 are cleared, the ID codeof the blue key 5A recorded in the immobilizer control unit 17 may bearranged to be cleared by the delete function, or the ID codes of theblue key A, the yellow key 5B and the green key 5D recorded in theimmobilizer control unit 17 may be arranged to be selectively cleared.For example, only the ID code in the immobilizer 17 corresponding to theyellow key 5B may be arranged to be deleted, or only the ID code in theimmobilizer 17 corresponding to the green key 5D may be arranged to bedeleted by the delete function.

Further, in the initialization mode of the above embodiment, althoughthe red key 5C can be formed from the commercially available engine key5, the cryptographic code other than the red key 5C recorded in theEEPROM 24 of the immobilizer control unit 17 may be arranged to becleared without forming the red key 5C in the control mode of theinitialization.

Further, in the initialization mode of the above embodiment, when the“initialization mode” is executed, the cryptographic codes other thanthe red key 5C recorded in the EEPROM 24 of the immobilizer control unit17 are finally cleared. However, in the case where the cryptographiccode of the blue key 5A is recorded in the EEPROM 24 of the immobilizercontrol unit 17 in “each key registration mode”, the immobilizer controlunit 17 may be arranged to be returned to the state before thecryptographic code of the blue key 5A of the EEPROM 24 recorded in theEEPROM 24 of the immobilizer control unit was registered when“initialization mode” is executed.

Further, in the case where the cryptographic code of the yellow key 5Bis recorded in the EEPROM 24 of the immobilizer control unit 17 in “eachkey registration mode”, the immobilizer control unit 17 may be arrangedto be returned to the state before the cryptographic code of the yellowkey 5A of the EEPROM 24 recorded in the EEPROM 24 of the immobilizercontrol unit was registered when “initialization mode” is executed.

Further, in the case where the cryptographic code of the green key 5D isrecorded in the EEPROM 24 of the immobilizer control unit 17 in “eachkey registration mode”, the immobilizer control unit 17 may be arrangedto be returned to the state before the cryptographic code of the greenkey 5D of the EEPROM 24 recorded in the EEPROM 24 of the immobilizercontrol unit was registered when “initialization mode” is executed.

Further, the initialization may be arranged to be performed as statedabove when the ID code of the red key 5C is collated with the ID coderecorded in the immobilizer control unit 17 corresponding thereto uponthe insertion of the red key 5C into the key cylinder 3 and the resultof the collation is affirmative.

Further, in the above embodiment, although the antitheft system of theinvention is applied to the work machine such as the backhoe, thevehicle to which the antitheft system of the invention is applied is notlimited to the work machine such as the backhoe, and it can also beapplied to an automobile and other vehicles.

According to the invention, since a new engine start key can be formedfrom a commercially available engine key through the start keyregistration function, in the case where the engine start key is lost,the new engine start key is formed without replacing the whole antitheftdevice, and the engine can be started by this new engine start key,which is economical and convenient. Further, since the allowance tool orthe allowance key to allow the rewriting or writing of thediscrimination code is required separately from the engine start key inorder to form the new engine start key, it is difficult for a personother than a user who purchased the vehicle to form the engine startkey, and the antitheft function of the antitheft system is not ruined.

INDUSTRIAL APPLICABILITY

The invention can be used for a work machine such as a backhoe and othervehicles.

1. An antitheft system for a vehicle configured to collate an ID code ofan engine start key (5A, 5B) with an ID code recorded in an immobilizercontrol unit (17), and to allow the engine start key (5A, 5B) to startan engine when a result of a collation is affirmative, the systemcomprising: an allowance tool (5C, 5D) for allowing rewriting or writingof an ID code, the allowance tool being provided separately from theengine start key (5A, 5B), the allowance tool (5C, 5D) being incapableof starting an engine while the engine start key (5A, 5B) beingincapable of allowing rewriting or writing of an ID code; and a startkey registration function of collating an ID code of the allowance tool(5C, 5D) with the ID code recorded in the immobilizer control unit (17)without starting engine and without requiring any special manipulationwith the key, and rendering an ID code of an engine key (5)corresponding to the ID code of the immobilizer control unit (17) whenthe result of the collation is affirmative, so that when the engine key(5) is inserted into a key cylinder (3), the inserted engine key (5)serves as the engine start key (5A, 5B).
 2. An antitheft system for avehicle according to claim 1, further comprising a copy function ofwriting the ID code of the allowance tool (5D) recorded in theimmobilizer control unit (17) into another member to cause the member toserve as an allowance tool.
 3. An antitheft system for a vehicleaccording to claim 1, wherein the ID code of the engine start key (5B)registered by the start key registration function can be recorded as anengine start key into an immobilizer control unit of another vehicle. 4.An antitheft system for a vehicle according to claim 3, furthercomprising a start key copy function of writing the ID code of theengine start key (5) into another engine key (5) to cause the engine keyto serve as the engine start key.
 5. An antitheft system for a vehicleaccording to claim 4, wherein the start key copy function of theimmobilizer control unit (17) writes the ID code of the engine start key(5B) into another engine key (5) to cause the engine key to serve as theengine start key, when the engine key (5) is inserted into a keycylinder (3) after the engine start key (5B) is inserted into the keycylinder (3).
 6. An antitheft system for a vehicle according to claim 4,wherein when a master key of the engine start key (5B) is inserted intoa key cylinder (3), a control mode for rendering the start key copyfunction operable is actuated.
 7. An antitheft system for a vehicleaccording to claim 1, further comprising a delete function of deletingthe ID code of the engine start key (5A, 5B) recorded in the immobilizercontrol unit (17) from the immobilizer control unit (17).
 8. Anantitheft system for a vehicle according to claim 1, further comprisingan engine start function with a special manipulation in which the engineis allowed to start when the engine key (5) is inserted into a keycylinder (3) and a special manipulation is performed.
 9. An antitheftsystem for a vehicle according to claim 1, further comprising aninitialization function in which an ID code recording portion of theimmobilizer control unit (17) is initialized.
 10. An antitheft systemfor a vehicle according to claim 1, wherein a vehicle to which theantitheft system is applied is a work machine such as a backhoe.
 11. Anantitheft system for a vehicle configured to collate an ID code of anengine start key (5A, 5B) with an ID code recorded in an immobilizercontrol unit (17), and to allow the engine start key (5A, 5B) to startan engine when a result of a collation is affirmative, or to prevent theengine start key (5A, 5B) from starting the engine when the result ofthe collation is negative, the system comprising: an allowance key (5C,5D) for allowing rewriting or writing of an ID code, the allowance keybeing provided separately from the engine start key (5A, 5B), theallowance key (5C, 5D) being incapable of starting an engine while theengine start key (5A, 5B) being incapable of allowing rewriting orwriting of an ID code; and a start key registration function ofcollating an ID code of the allowance key (5C, 5D) with the ID coderecorded in the immobilizer control unit (17) without starting engineand without requiring any special manipulation with the key, andrendering an ID code of an engine key (5) corresponding to the ID codeof the immobilizer control unit (17) when the result of the collation isaffirmative, so that when the engine key (5) is inserted into a keycylinder (3), the inserted engine key (5) serves as the engine start key(5A, 5B).
 12. An antitheft system for a vehicle according to claim 11,wherein the start key registration function renders the ID code of theengine key (5) corresponding to the ID code of the immobilizer controlunit (17), when the engine key (5) is inserted into a key cylinder (3)after the allowance key (5C, 5D) is inserted into the key cylinder (3),so that the engine key (5) serves as the engine start key (5A, 5B). 13.An antitheft system for a vehicle according to claim 11, furthercomprising an allowance key copy function of writing the ID code of theallowance key (5D) into another engine key (5) to cause the engine keyto serve as an allowance key.
 14. An antitheft system for a vehicleaccording to claim 13, wherein the allowance key copy function of theimmobilizer control unit (17) writes the ID code of the allowance key(5D) into another engine key (5) to cause the engine key to serve as theallowance key, when the engine key (5) is inserted into a key cylinder(3) after the allowance key (5D) is inserted into the key cylinder (3).15. An antitheft system for a vehicle according to claim 13, whereinwhen a master key of the allowance key (5D) is inserted into a keycylinder (3), a control mode for rendering the allowance key copyfunction operable is actuated.
 16. An antitheft system for a vehicleaccording to claim 11, wherein after the allowance key (5C, 5D) isinserted into a key cylinder (3), the ID code of the allowance key (5C,5D) is collated with the ID code recorded in the immobilizer controlunit (17), and when the result of the collation is affirmative, acontrol mode for rendering the start key registration function operableis actuated.
 17. An antitheft system for a vehicle configured to collatean ID code of an engine start key (5A, 5B) with an ID code recorded inan immobilizer control unit (17), and to allow the engine start key (5A,5B) to start an engine when a result of a collation is affirmative, orto prevent the engine start key (5A, 5B) from starting the engine whenthe result of the collation is negative, the system comprising: anallowance key (5C, 5D) for allowing rewriting or writing of an 11) code,the allowance key being provided separately from the engine start key(5A, 5B), the allowance key (5C, 5D) being incapable of starting anengine while the engine start key (5A, 5B) being incapable of allowingrewriting or writing of an ID code; a start key registration function ofcollating an ID code of the allowance key (5C, 5D) with the ID coderecorded in the immobilizer control unit (17) without starting engineand without requiring any special manipulation with the key, andrendering an ID code of an engine key (5) corresponding to the ID codeof the immobilizer control unit (17) when the result of the collation isaffirmative, so that when the engine key (5) is inserted into a keycylinder (3), the inserted engine key (5) serves as the engine start key(5A, 5B); and a cryptographic code for specifying the engine key (5) andan discrimination code for distinguishing kind of the engine key (5)recorded as ID codes in the engine key (5) and the immobilizer controlunit (17), the discrimination code enabling the system to distinguishthe engine start key (5A, 5B) for starting the engine and the allowancekey (5C, 5D) for allowing the rewriting or writing of the ID codes.